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1
Ricci, Anthony. « Differences in Mechano-Transducer Channel Kinetics Underlie Tonotopic Distribution of Fast Adaptation in Auditory Hair Cells ». Journal of Neurophysiology 87, no 4 (1 avril 2002) : 1738–48. http://dx.doi.org/10.1152/jn.00574.2001.
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The first step in audition is a deflection of the sensory hair bundle that opens mechanically gated channels, depolarizing the sensory hair cells. Two mechanism of adaptation of mechano-electric transducer (MET) channels have been identified in turtle auditory hair cells. The rate of fast adaptation varies tonotopically and is postulated to underlie a mechanical tuning mechanism in turtle auditory hair cells. Fast adaptation is driven by a calcium-dependent feedback process associated with MET channels. The purpose of this paper is to test the hypothesis that fast adaptation contributes to MET channel kinetics and that variations in channel kinetics underlie the tonotopic distribution of fast adaptation. To test for kinetic differences, the open channel blocker dihydrostreptomycin (DHS) was used. DHS blocked MET currents from low-frequency cells (IC50 = 14 ± 2 μM) more effectively than high-frequency cells (IC50 = 75 ± 5 μM), suggesting differences in MET channel properties. DHS block showed similar calcium sensitivities at both papilla locations. No difference in calcium permeation or block of the transducer channels was observed, indicating that the DHS effect was not due to differences in the channel pore. Slowing adaptation increased DHS efficacy, and speeding adaptation decreased DHS efficacy, suggesting that adaptation was influencing DHS block. DHS block of MET channels slowed adaptation, most likely by reducing the peak intraciliary calcium concentration achieved, supporting the hypothesis that the rate of adaptation varies with the calcium load per stereocilia. Another channel blocker, amiloride showed similar efficacy for high- and low-frequency cells with an IC50 of 24.2 ± 0.5 μM and a Hill coefficient of 2 but appeared to block high-frequency channels faster than low-frequency channels. To further explore MET channel differences between papilla locations, stationary noise analysis was performed. Spectral analysis of the noise gave half power frequencies of 1,185 ± 148 Hz ( n = 6) and 551 ± 145 Hz ( n = 5) for high- and low-frequency cells in 2.8 mM external calcium. The half power frequency showed similar calcium sensitivity to that of adaptation shifting to 768 ± 205 Hz ( n = 4) and 289 ± 63 Hz ( n = 4) for high- and low-frequency cells in 0.25 mM external calcium. Both the pharmacological data and the noise analysis data are consistent with the hypothesis that the tonotopic distribution of fast adaptation is in part due to differences in MET channel kinetics. An increase in the number of MET channels per stereocilia (termed summation) and or intrinsic differences in MET channel kinetics may be the underlying mechanism involved in establishing the gradient.
2
Small, D. L., et C. E. Morris. « Delayed activation of single mechanosensitive channels in Lymnaea neurons ». American Journal of Physiology-Cell Physiology 267, no 2 (1 août 1994) : C598—C606. http://dx.doi.org/10.1152/ajpcell.1994.267.2.c598.
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Some stretch-activated (SA) channels challenged with suction jumps exhibit adaptation, a dynamic behavior that can be overlooked because of its mechanical fragility. In previous studies of neuronal SA K channels, we detected no adaptation, but the protocols used were not designed to detect dynamics. Here, we reproduce the adaptation seen by others in Xenopus SA cationic (Cat) channels but show that, with the same protocol, no adaptation occurs with SA K channels. Instead, SA K channels exhibit a different dynamic behavior, delayed activation. Lymnaea SA K channels subjected to pressure jumps responded after a 1- to 4-s delay with a gradual, rather than abrupt, onset of activation. The delay was pressure dependent and was longer for patches from older cultured neurons. Delayed responses were fragile like SA Cat channel adaptation; they disappeared with repeated stimuli. Cytochalasin D decreased the delay and increased the stretch activation of SA K channels. Unlike SA Cat channel adaptation, which occurs only at hyperpolarized potentials, SA K channel delay was not voltage dependent. We note that once SA Cat and SA K channels are "stripped" of their fragile (cytoskeleton-dependent?) dynamics, however, their gating behaviors show little fundamental difference; both are stretch activatable and have a higher open probability at depolarized potentials.
3
Geiser, Florian, Daniel Wessel, Matthias Hummert, Andreas Weber, Dirk Wübben, Armin Dekorsy et Alberto Viseras. « DRLLA : Deep Reinforcement Learning for Link Adaptation ». Telecom 3, no 4 (23 novembre 2022) : 692–705. http://dx.doi.org/10.3390/telecom3040037.
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Link adaptation (LA) matches transmission parameters to conditions on the radio link, and therefore plays a major role in telecommunications. Improving LA is within the requirements for next-generation mobile telecommunication systems, and by refining link adaptation, a higher channel efficiency can be achieved (i.e., an increased data rate thanks to lower required bandwidth). Furthermore, by replacing traditional LA algorithms, radio transmission systems can better adapt themselves to a dynamic environment. There are several drawbacks to current state-of-the-art approaches, including predefined and static decision boundaries or relying on a single, low-dimensional metric. Nowadays, a broadly used approach to handle a variety of related input variables is a neural network (NN). NNs are able to make use of multiple inputs, and when combined with reinforcement learning (RL), the so-called deep reinforcement learning (DRL) approach emerges. Using DRL, more complex parameter relationships can be considered in order to recommend the modulation and coding scheme (MCS) used in LA. Hence, this work examines the potential of DRL and includes experiments on different channels. The main contribution of this work lies in using DRL algorithms for LA, optimized for throughput based on a subcarrier observation matrix and a packet success rate feedback system. We apply Natural Actor-Critic (NAC) and Proximal Policy Optimization (PPO) algorithms on simulated channels with a subsequent feasibility study on a prerecorded real-world channel. Empirical results produced by experiments on the examined channels hint that Deep Reinforcement Learning for Link Adaptation (DRLLA) offers good performance indicated by a promising data rate on the additive white Gaussian noise (AWGN) channel, the non-line-of-sight (NLOS) channel, and a prerecorded real-world channel. No matter the channel impairment, the agent is able to respond to changing signal-to-interference-plus-noise-ratio (SINR) levels, as exhibited by expected changes in the effective data rate.
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Yang, Ge, Chao Zhang, Ling Gao, Yufei Guo et Jinyang Guo. « Domain Adaptive Channel Pruning ». Electronics 13, no 5 (26 février 2024) : 887. http://dx.doi.org/10.3390/electronics13050887.
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Domain adaptation is an effective approach to improve the generalization ability of deep learning methods, which makes a deep model more stable and robust. However, these methods often suffer from a deployment problem when deep models are deployed on different types of edge devices. In this work, we propose a new channel pruning method called Domain Adaptive Channel Pruning (DACP), which is specifically designed for the unsupervised domain adaptation task, where there is considerable data distribution mismatch between the source and the target domains. We prune the channels and adjust the weights in a layer-by-layer fashion. In contrast to the existing layer-by-layer channel pruning approaches that only consider how to reconstruct the features from the next layer, our approach aims to minimize both classification error and domain distribution mismatch. Furthermore, we propose a simple but effective approach to utilize the unlabeled data in the target domain. Our comprehensive experiments on two benchmark datasets demonstrate that our newly proposed DACP method outperforms the existing channel pruning approaches under the unsupervised domain adaptation setting.
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Wichmann, Lukas, et Mike Althaus. « Evolution of epithelial sodium channels : current concepts and hypotheses ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 319, no 4 (1 octobre 2020) : R387—R400. http://dx.doi.org/10.1152/ajpregu.00144.2020.
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The conquest of freshwater and terrestrial habitats was a key event during vertebrate evolution. Occupation of low-salinity and dry environments required significant osmoregulatory adaptations enabling stable ion and water homeostasis. Sodium is one of the most important ions within the extracellular liquid of vertebrates, and molecular machinery for urinary reabsorption of this electrolyte is critical for the maintenance of body osmoregulation. Key ion channels involved in the fine-tuning of sodium homeostasis in tetrapod vertebrates are epithelial sodium channels (ENaCs), which allow the selective influx of sodium ions across the apical membrane of epithelial cells lining the distal nephron or the colon. Furthermore, ENaC-mediated sodium absorption across tetrapod lung epithelia is crucial for the control of liquid volumes lining the pulmonary surfaces. ENaCs are vertebrate-specific members of the degenerin/ENaC family of cation channels; however, there is limited knowledge on the evolution of ENaC within this ion channel family. This review outlines current concepts and hypotheses on ENaC phylogeny and discusses the emergence of regulation-defining sequence motifs in the context of osmoregulatory adaptations during tetrapod terrestrialization. In light of the distinct regulation and expression of ENaC isoforms in tetrapod vertebrates, we discuss the potential significance of ENaC orthologs in osmoregulation of fishes as well as the putative fates of atypical channel isoforms in mammals. We hypothesize that ancestral proton-sensitive ENaC orthologs might have aided the osmoregulatory adaptation to freshwater environments whereas channel regulation by proteases evolved as a molecular adaptation to lung liquid homeostasis in terrestrial tetrapods.
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Pejoski, Slavche, et Venceslav Kafedziski. « Cross-Layer Framework for Multiuser Real Time H.264/AVC Video Encoding and Transmission over Block Fading MIMO Channels Using Outage Probability ». Advances in Multimedia 2014 (2014) : 1–10. http://dx.doi.org/10.1155/2014/362196.
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We present a framework for cross-layer optimized real time multiuser encoding of video using a single layer H.264/AVC and transmission over MIMO wireless channels. In the proposed cross-layer adaptation, the channel of every user is characterized by the probability density function of its channel mutual information and the performance of the H.264/AVC encoder is modeled by a rate distortion model that takes into account the channel errors. These models are used during the resource allocation of the available slots in a TDMA MIMO communication system with capacity achieving channel codes. This framework allows for adaptation to the statistics of the wireless channel and to the available resources in the system and utilization of the multiuser diversity of the transmitted video sequences. We show the effectiveness of the proposed framework for video transmission over Rayleigh MIMO block fading channels, when channel distribution information is available at the transmitter.
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Rice, Joseph, Richard Shockley, Dale Green, John Proakis et Milica Stojanovic. « Telesonar channel estimation and adaptation ». Journal of the Acoustical Society of America 105, no 2 (février 1999) : 1364. http://dx.doi.org/10.1121/1.426462.
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Ivanov, D. V., V. A. Ivanov, N. V. Ryabova et A. A. Kislitsyn. « Implementation of the Maximum Bandwidth Ratio of Satellite Radio Communication Systems under the Conditions for Intramodal Dispersion of Transionospheric Radio Channels ». Радиотехника и электроника 68, no 6 (1 juin 2023) : 571–78. http://dx.doi.org/10.31857/s0033849423060049.
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The problem of significant extension of the band of the transionospheric radio channel to the maximum possible values is solved to improve the efficiency of satellite communication systems. Hardware and software are created to suppress the group delay dispersion using methods of data mining for experimental diagnostics of a transionospheric communication line. Algorithms and tools for intelligent sensory diagnostics of wideband radio channels with adaptation to dispersion variability are developed. In the absence of adaptation, it is possible to create radio channels of undistorted transmission with a bandwidth ratio of no greater than 4.5%, while adaptation to dispersion variability makes it possible to increase the bandwidth ratio to 11.5%. The greatest bandwidth ratio (20–25%) for dispersion-free transmission can be achieved with the aid of adaptive inverse filtering of the channel frequency response in combination with such intelligent methods as equalization with error, machine learning of channel equalizer, and big data processing.
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Li, Shuang, Chi Liu, Qiuxia Lin, Binhui Xie, Zhengming Ding, Gao Huang et Jian Tang. « Domain Conditioned Adaptation Network ». Proceedings of the AAAI Conference on Artificial Intelligence 34, no 07 (3 avril 2020) : 11386–93. http://dx.doi.org/10.1609/aaai.v34i07.6801.
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Tremendous research efforts have been made to thrive deep domain adaptation (DA) by seeking domain-invariant features. Most existing deep DA models only focus on aligning feature representations of task-specific layers across domains while integrating a totally shared convolutional architecture for source and target. However, we argue that such strongly-shared convolutional layers might be harmful for domain-specific feature learning when source and target data distribution differs to a large extent. In this paper, we relax a shared-convnets assumption made by previous DA methods and propose a Domain Conditioned Adaptation Network (DCAN), which aims to excite distinct convolutional channels with a domain conditioned channel attention mechanism. As a result, the critical low-level domain-dependent knowledge could be explored appropriately. As far as we know, this is the first work to explore the domain-wise convolutional channel activation for deep DA networks. Moreover, to effectively align high-level feature distributions across two domains, we further deploy domain conditioned feature correction blocks after task-specific layers, which will explicitly correct the domain discrepancy. Extensive experiments on three cross-domain benchmarks demonstrate the proposed approach outperforms existing methods by a large margin, especially on very tough cross-domain learning tasks.
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Belyy, Vladislav, Kishore Kamaraju, Bradley Akitake, Andriy Anishkin et Sergei Sukharev. « Adaptive behavior of bacterial mechanosensitive channels is coupled to membrane mechanics ». Journal of General Physiology 135, no 6 (31 mai 2010) : 641–52. http://dx.doi.org/10.1085/jgp.200910371.
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Mechanosensitive channel of small conductance (MscS), a tension-driven osmolyte release valve residing in the inner membrane of Escherichia coli, exhibits a complex adaptive behavior, whereas its functional counterpart, mechanosensitive channel of large conductance (MscL), was generally considered nonadaptive. In this study, we show that both channels exhibit similar adaptation in excised patches, a process that is completely separable from inactivation prominent only in MscS. When a membrane patch is held under constant pressure, adaptation of both channels is manifested as a reversible current decline. Their dose–response curves recorded with 1–10-s ramps of pressure are shifted toward higher tension relative to the curves measured with series of pulses, indicating decreased tension sensitivity. Prolonged exposure of excised patches to subthreshold tensions further shifts activation curves for both MscS and MscL toward higher tension with similar magnitude and time course. Whole spheroplast MscS recordings performed with simultaneous imaging reveal activation curves with a midpoint tension of 7.8 mN/m and the slope corresponding to ∼15-nm2 in-plane expansion. Inactivation was retained in whole spheroplast mode, but no adaptation was observed. Similarly, whole spheroplast recordings of MscL (V23T mutant) indicated no adaptation, which was present in excised patches. MscS activities tried in spheroplast-attached mode showed no adaptation when the spheroplasts were intact, but permeabilized spheroplasts showed delayed adaptation, suggesting that the presence of membrane breaks or edges causes adaptation. We interpret this in the framework of the mechanics of the bilayer couple linking adaptation of channels in excised patches to the relaxation of the inner leaflet that is not in contact with the glass pipette. Relaxation of one leaflet results in asymmetric redistribution of tension in the bilayer that is less favorable for channel opening.
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Chatterjee, Shampa, Abu-Bakr Al-Mehdi, Irena Levitan, Troy Stevens et Aron B. Fisher. « Shear stress increases expression of a KATP channel in rat and bovine pulmonary vascular endothelial cells ». American Journal of Physiology-Cell Physiology 285, no 4 (octobre 2003) : C959—C967. http://dx.doi.org/10.1152/ajpcell.00511.2002.
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We have shown previously that acute ischemia leads to depolarization of pulmonary microvascular endothelial cells that is prevented with cromakalim, suggesting the presence of ATP-sensitive K+ (KATP) channels in these cells. Thus KATP channel expression and activity were evaluated in rat pulmonary microvascular endothelial cells (RPMVEC) by whole cell current measurements, dot blot (mRNA), and immunoblot (protein) for the inwardly rectifying K+ channel (KIR) 6.2 subunit and fluorescent ligand binding for the sulfonylurea receptor (SUR). Low-level expression of a KATP channel was detected in endothelial cells in routine (static) culture and led us to examine whether its expression is inducible when endothelial cells are adapted to flow. Channel expression (mRNA and both KIR6.2 and SUR proteins) and inwardly rectified membrane current by patch clamp increased significantly when RPMVEC were adapted to flow at 10 dyn/cm2 for 24 h in either a parallel plate flow chamber or an artificial capillary system. Induction of the KATP channel with flow adaptation was also observed in bovine pulmonary artery endothelial cells. Flow-adapted but not static RPMVEC showed cellular plasma membrane depolarization upon stop of flow that was inhibited by a KATP channel opener and prevented by addition of cycloheximide to the medium during the flow adaptation period. These studies indicate the induction of KATP channels by flow adaptation in pulmonary endothelium and that the expression and activity of this channel are essential for the endothelial cell membrane depolarization response with acute decrease in shear stress.
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HEINRICH, THOMAS STEPHAN, et MICHAEL BACH. « Contrast adaptation in retinal and cortical evoked potentials : No adaptation to low spatial frequencies ». Visual Neuroscience 19, no 5 (septembre 2002) : 645–50. http://dx.doi.org/10.1017/s0952523802195095.
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Contrast adaptation occurs in both the retina and the cortex. Defining its spatial dependence is crucial for understanding its potential roles. We thus asked to what degree contrast adaptation depends on spatial frequency, including cross-adaptation. Measuring the pattern electroretinogram (PERG) and the visual evoked potential (VEP) allowed separating retinal and cortical contributions. In ten subjects we recorded simultaneous PERGs and VEPs. Test stimuli were sinusoidal gratings of 98% contrast with spatial frequencies of 0.5 or 5.0 cpd, phase reversing at 17 reversals/s. Adaptation was controlled by prolonged presentation of these test stimuli or homogenous gray fields of the same luminance. When adaptation and test frequency were identical, we observed significant contrast adaptation only at 5 cpd: an amplitude reduction in the PERG (−22%) and VEP (−58%), and an effective reduction of latency in the PERG (−0.95 ms). When adapting at 5 cpd and testing at 0.5 cpd, the opposite effect was observed: enhancement of VEP amplitude by +26% and increase in effective PERG latency by +1.35 ms. When adapting at 0.5 cpd and testing at 5 cpd, there was no significant amplitude change in PERG and VEP, but a small effective PERG latency increase of +0.65 ms. The 0.5-cpd channel was not adapted by spatial frequencies of 0.5 cpd. The adaptability of the 5-cpd channel may mediate improved detail recognition after prolonged blur. The existence of both adaptable and nonadaptable mechanisms in the retina allows for the possibility that by comparing the adaptational state of spatial-frequency channels the retina can discern between overall low contrast and defocus in emmetropization control.
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Perry, Matthew D., Vazhaikkurichi M. Rajendran, Kenneth A. MacLennan et Geoffrey I. Sandle. « Segmental differences in upregulated apical potassium channels in mammalian colon during potassium adaptation ». American Journal of Physiology-Gastrointestinal and Liver Physiology 311, no 5 (1 novembre 2016) : G785—G793. http://dx.doi.org/10.1152/ajpgi.00181.2015.
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Rat proximal and distal colon are net K+secretory and net K+absorptive epithelia, respectively. Chronic dietary K+loading increases net K+secretion in the proximal colon and transforms net K+absorption to net K+secretion in the distal colon, but changes in apical K+channel expression are unclear. We evaluated expression/activity of apical K+(BK) channels in surface colonocytes in proximal and distal colon of control and K+-loaded animals using patch-clamp recording, immunohistochemistry, and Western blot analyses. In controls, BK channels were more abundant in surface colonocytes from K+secretory proximal colon (39% of patches) than in those from K+-absorptive distal colon (12% of patches). Immunostaining demonstrated more pronounced BK channel α-subunit protein expression in surface cells and cells in the upper 25% of crypts in proximal colon, compared with distal colon. Dietary K+loading had no clear-cut effects on the abundance, immunolocalization, or expression of BK channels in proximal colon. By contrast, in distal colon, K+loading 1) increased BK channel abundance in patches from 12 to 41%; 2) increased density of immunostaining in surface cells, which extended along the upper 50% of crypts; and 3) increased expression of BK channel α-subunit protein when assessed by Western blotting ( P < 0.001). Thus apical BK channels are normally more abundant in K+secretory proximal colon than in K+absorptive distal colon, and apical BK channel expression in distal (but not proximal) colon is greatly stimulated as part of the enhanced K+secretory response to dietary K+loading.
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Mohd Anuar, Aliya Syahira, Wan Norsyafizan W. Muhamad, Darmawaty Mohd Ali, Suzi Seroja Sarnin et Norfishah Ab Wahab. « A review on link adaptation techniques for energy efficiency and QoS in IEEE802.11 WLAN ». Indonesian Journal of Electrical Engineering and Computer Science 17, no 1 (1 janvier 2020) : 331. http://dx.doi.org/10.11591/ijeecs.v17.i1.pp331-339.
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<span>Link adaptation is a technique that able to adapt modulation and coding scheme (MCS) based on radio channel conditions. With the exponential increase on the wireless devices nowadays, it contributes to high energy consumption and an increase in carbon dioxide (CO<sub>2</sub>) emission which contribute to the environmental issue. Researchers have developed proposals to tackle these issues by design algorithms based on link adaptation technique. Nowadays, various link adaptation techniques have been proposed by researchers with target for either Quality of Service (QoS) enhancement as well as energy efficiency. This paper presents A Review on Link Adaptation Techniques for Energy Efficiency and QoS in IEEE802.11 WLAN. In this study, a comprehensive review of the relevant literature published that focus on link adaptation technique in IEEE 802.11 WLAN in improving the energy efficiency and maximize the QoS performance is presented. Link adaptation can be categorized into transmission power control adaptation, transmission data rate adaptation and joint rate adaptation. These adaptations are carried out according to the channel state information (CSI). CSI can be categorized into signal-to-noise ratio (SNR), bit error rate (BER), delay, and queue length.</span>
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Cheng, H., M. Fill, H. Valdivia et W. Lederer. « Models of Ca2+ release channel adaptation ». Science 267, no 5206 (31 mars 1995) : 2009–10. http://dx.doi.org/10.1126/science.7701326.
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Sachs, F., F. Qin et P. Palade. « Models of Ca2+ release channel adaptation ». Science 267, no 5206 (31 mars 1995) : 2010–11. http://dx.doi.org/10.1126/science.7701327.
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Beurg, Maryline, Adam C. Goldring et Robert Fettiplace. « The effects of Tmc1 Beethoven mutation on mechanotransducer channel function in cochlear hair cells ». Journal of General Physiology 146, no 3 (31 août 2015) : 233–43. http://dx.doi.org/10.1085/jgp.201511458.
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Sound stimuli are converted into electrical signals via gating of mechano-electrical transducer (MT) channels in the hair cell stereociliary bundle. The molecular composition of the MT channel is still not fully established, although transmembrane channel–like protein isoform 1 (TMC1) may be one component. We found that in outer hair cells of Beethoven mice containing a M412K point mutation in TMC1, MT channels had a similar unitary conductance to that of wild-type channels but a reduced selectivity for Ca2+. The Ca2+-dependent adaptation that adjusts the operating range of the channel was also impaired in Beethoven mutants, with reduced shifts in the relationship between MT current and hair bundle displacement for adapting steps or after lowering extracellular Ca2+; these effects may be attributed to the channel’s reduced Ca2+ permeability. Moreover, the density of stereociliary CaATPase pumps for Ca2+ extrusion was decreased in the mutant. The results suggest that a major component of channel adaptation is regulated by changes in intracellular Ca2+. Consistent with this idea, the adaptive shift in the current–displacement relationship when hair bundles were bathed in endolymph-like Ca2+ saline was usually abolished by raising the intracellular Ca2+ concentration.
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Moltchanov, D. « Cross-layer performance control of wireless channels using active local profiles ». Journal of Communications Software and Systems 3, no 3 (22 septembre 2007) : 148. http://dx.doi.org/10.24138/jcomss.v3i3.250.
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To optimize performance of applications running over wireless channels state-of-the-art wireless access technologies incorporate a number of channel adaptation mechanisms. While these mechanisms are expected to operate jointly providing the best possible performance for current wireless channel and traffic conditions, their joint effect is often difficult to predict. To control functionality of various channel adaptation mechanisms a new cross-layer performance optimization system is sought. This system should be responsible for exchange of control informationbetween different layers and further optimization of wireless channel performance. In this paper design of the cross-layer performance control system for wireless access technologies with dynamic adaptation of protocol parameters at different layers of the protocol stack is proposed. Functionalities of components of the system are isolated and described in detail. To determine the range of protocol parameters providing the best possible performance for a wide range of channel and arrival statistics the proposed system is analytically analyzed. Particularly, probability distribution functions of the number of lost frames and delay of a frame as functions of first- and second-order wireless channel and arrival statistics, automatic repeat request, forward error correction functionality, protocol data unit size at different layers are derived. Numerical examples illustrating performance of the whole system and its elements are provided. Obtainedresults demonstrate that the proposed system provide significant performance gains compared to static configuration of protocols.
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Travediu, Ana-Maria. « Improve channel signal quality using adaptive filters ». Scientific Bulletin of Naval Academy XXIII, no 1 (15 juillet 2020) : 90–96. http://dx.doi.org/10.21279/1454-864x-20-i1-012.
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A channel can be modelled by trying to calculate the physical processes which modify the transmitted signal. In this article we simulated the adaptive equalization of some communication channels. A system of data transmission in the basic band will be considered in order to illustrate the principle of adaptive equalization. In such a system, the data sequence is applied, upon emission, to a formation filter( low pass filter), with the purpose of limiting the occupied bandwidth. A relatively wide band noise is also introduced on the communication channel. The transmission channel can also be modelled as a linear filter, this is represented by the distortion filter. We used another filter to avoid the distortion introduced by the channel, with the role of equalizer. This should compensate for the distortion introduced by the channel. The channel transfer function is not generally known, and in addition, it may vary slowly over time. Therefore, the need for this filter appears to be adaptive. In order to perform the adaptation initially, a training sequence, known at the reception, can be transmitted first and the output of the filter is compared with a locally generated reference signal, but identical to the one emitted. After this initial adaptation phase, the transmitter transmits the information symbols, the useful signal, thus the application can be used to improve the signal quality of maritime communications channels.
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Gupta, Vivek K., Ammaji Rajala et Raju V. S. Rajala. « Insulin receptor regulates photoreceptor CNG channel activity ». American Journal of Physiology-Endocrinology and Metabolism 303, no 11 (1 décembre 2012) : E1363—E1372. http://dx.doi.org/10.1152/ajpendo.00199.2012.
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Photoreceptor cyclic nucleotide gated (CNG) channels are critical elements in phototransduction and light adaptation. Here we report that insulin receptor (IR), an integral membrane protein, directly phosphorylates the CNGA1 subunit of CNG channels that in turn affects the function of these channels negatively. The IR phosphorylates Tyr498 and Tyr503 residues on CNGA1 that are situated at the membrane-cytoplasmic interface. The IR tyrosine kinase activity is essential for the inhibition of CNG channel. To maintain the channels in an off state, it is necessary not only to have a precise balance of the cGMP levels but also to have a control on the cGMP sensitivity of the CNG channels itself. In this study, we observed that the channel opens at a lower concentration of cGMP in IR−/− mice. These studies suggest that IR regulates the modulation of CNG channel activity in vivo.
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Huang, Tingpei, Shibao Li, Xiaoxuan Lu et Shaoshu Gao. « An Interference-Aware Rate and Channel Adaptation Scheme for Dense IEEE 802.11n Networks ». Wireless Communications and Mobile Computing 2019 (3 avril 2019) : 1–14. http://dx.doi.org/10.1155/2019/1902463.
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Rate adaptation, which dynamically chooses transmission rate provided at the physical layer according to the current channel conditions, is a fundamental resource management issue in IEEE 802.11 networks with the goal of maximizing the network throughput. Traditional rate adaptation algorithms for IEEE 802.11n networks do not consider the interference problem, which becomes much more serious due to the rapid deployment of IEEE 802.11n devices and large number of mobile terminals. In this paper, an interference-aware rate and channel adaptation scheme RaCA for intensive IEEE 802.11n networks was proposed. Firstly, RaCA leverages RSSI and CSI information together to measure the current channel conditions at the receiver side. RSSI is a coarse-grained indicator and CSI is a fine-grained indicator. Secondly, a two-stage rate adaptation scheme TSRA was designed, which can quickly adapt to optimal bit rate based on RSSI and CSI information. Finally, a quorum-based channel adaptation algorithm QCA was proposed, which does not need control channel. If channel suffers severe interferences, RaCA calls QCA to choose another channel to work on. Simulation and testbed implementation results demonstrate that RaCA achieves significant throughput gain over SampleLite and Minstrel-HT.
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Okamura, Yasushi, Atsuo Nishino, Yoshimichi Murata, Koichi Nakajo, Hirohide Iwasaki, Yukio Ohtsuka, Motoko Tanaka-Kunishima et al. « Comprehensive analysis of the ascidian genome reveals novel insights into the molecular evolution of ion channel genes ». Physiological Genomics 22, no 3 (11 août 2005) : 269–82. http://dx.doi.org/10.1152/physiolgenomics.00229.2004.
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Ion fluxes through membrane ion channels play crucial roles both in neuronal signaling and the homeostatic control of body electrolytes. Despite our knowledge about the respective ion channels, just how diversification of ion channel genes underlies adaptation of animals to the physical environment remains unknown. Here we systematically survey up to 160 putative ion channel genes in the genome of Ciona intestinalis and compare them with corresponding gene sets from the genomes of the nematode Chaenorhabditis elegans, the fruit fly Drosophila melanogaster, and the more closely related genomes of vertebrates. Ciona has a set of so-called “prototype” genes for ion channels regulating neuronal excitability, or for neurotransmitter receptors, suggesting that genes responsible for neuronal signaling in mammals appear to have diversified mainly via gene duplications of the more restricted members of ancestral genomes before the ascidian/vertebrate divergence. Most genes responsible for modulation of neuronal excitability and pain sensation are absent from the ascidian genome, suggesting that these genes arose after the divergence of urochordates. In contrast, the divergent genes encoding connexins, transient receptor potential-related channels and chloride channels, channels involved rather in homeostatic control, indicate gene duplication events unique to the ascidian lineage. Because several invertebrate-unique channel genes exist in Ciona genome, the crown group of extant vertebrates not only acquired novel channel genes via gene/genome duplications but also discarded some ancient genes that have persisted in invertebrates. Such genome-wide information of ion channel genes in basal chordates enables us to begin correlating the innovation and remodeling of genes with the adaptation of more recent chordates to their physical environment.
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Holub, Jan, Oldřich Slavata, Pavel Souček, Odysseas Zisimopoulos, Dimitris Toumpakaris et Stavros Kotsopoulos. « Towards Layer Adaptation for Audio Transmission ». International Journal of Interdisciplinary Telecommunications and Networking 6, no 4 (octobre 2014) : 35–41. http://dx.doi.org/10.4018/ijitn.2014100104.
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When audio is transmitted over the wireless channel, the quality of the audio depends on the signal-to-noise ratio (SNR). The purpose of this paper is to investigate if rate adaptation can be avoided, and a system can rely instead on the audio encoder and decoder to alleviate the effect of channel errors. To this end, the paper reports on a set of experiments on various combinations of channel conditions, constellation sizes and audio encoding used and on the final audio quality achieved. The Mean Opinion Score (MOS) is used for performance evaluation. The MOS values are generated using the ITU-T P.862 (PESQ) and P.863 (POLQA) algorithms, and also using tests by experts. The results support the common practice of adapting the physical layer parameters to changing channel conditions. However, in some cases, it is possible to maintain a constant rate without impacting significantly the quality of the audio. This means that the complexity associated with physical layer and audio rate adaptation can be avoided leading to simpler and more robust designs.
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Evtushenko, Anna A., Irina P. Voronova et Tamara V. Kozyreva. « Effect of Long-Term Adaptation to Cold and Short-Term Cooling on the Expression of the TRPM2 Ion Channel Gene in the Hypothalamus of Rats ». Current Issues in Molecular Biology 45, no 2 (20 janvier 2023) : 1002–11. http://dx.doi.org/10.3390/cimb45020065.
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The present study is aimed to elucidate the possible involvement of the thermosensitive TRPM2 ion channel in changing of the temperature sensitivity of the hypothalamus after different cold exposures—long-term adaptation to cold and short-term cooling. Quantitative RT-PCR was used to study the expression of the gene of thermosensitive TRPM2 ion channel in the hypothalamus in the groups of control (kept for 5 weeks at +20 to +22 °C) and cold-adapted (5 weeks at +4 to +6 °C) rats, as well as in the groups of animals which were subjected to acute cooling (rapid or slow) with subsequent restoration of body temperature to the initial level. It has been shown that after long-term adaptation to cold, the decrease in the Trpm2 gene expression was observed in the hypothalamus, while a short-term cooling does not affect the expression of the gene of this ion channel. Thus, long-term adaptation to cold results in the decrease in the activity not only of the TRPV3 ion channel gene, as shown earlier, but also of the Trpm2 gene in the hypothalamus. The overlapping temperature ranges of the functioning of these ion channels and their unidirectional changes during the adaptation of the homoeothermic organism to cold suggest their functional interaction. The decrease in the Trpm2 gene expression may indicate the participation of this ion channel in adaptive changes in hypothalamic thermosensitivity, but only as a result of long-term cold exposure and not of a short-term cooling. These processes occurring at the genomic level are one of the molecular mechanisms of the adaptive changes.
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Bej, Aritra, et James B. Ames. « Retinal Cyclic Nucleotide-Gated Channel Regulation by Calmodulin ». International Journal of Molecular Sciences 23, no 22 (16 novembre 2022) : 14143. http://dx.doi.org/10.3390/ijms232214143.
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Retinal cyclic nucleotide-gated (CNG) ion channels bind to intracellular cGMP and mediate visual phototransduction in photoreceptor rod and cone cells. Retinal rod CNG channels form hetero-tetramers comprised of three CNGA1 and one CNGB1 protein subunits. Cone CNG channels are similar tetramers consisting of three CNGA3 and one CNGB3 subunits. Calmodulin (CaM) binds to two distinct sites (CaM1: residues 565–587 and CaM2: residues 1120–1147) within the cytosolic domains of rod CNGB1. The binding of Ca2+-bound CaM to CNGB1 promotes the Ca2+-induced desensitization of CNG channels in retinal rods that may be important for photoreceptor light adaptation. Mutations that affect Ca2+-dependent CNG channel function are responsible for inherited forms of blindness. In this review, we propose structural models of the rod CNG channel bound to CaM that suggest how CaM might cause channel desensitization and how dysregulation of the channel may lead to retinal disease.
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Ali, Muhmmad, Ihab M. Ali Almaameri, Abdul Malik, Fahim Khan, Muhammad Khalid Rabbani et Alamgir. « Link Adaptation Strategy for Underwater Acoustic Sensor Networks : A Machine Learning Approach ». Journal of Smart Internet of Things 1, no 1 (1 juin 2023) : 56–64. http://dx.doi.org/10.2478/jsiot-2023-0006.
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Abstract Due to growing concerns regarding their use in fields including oceanography, commercial marine operations, and military surveillance, demand in the exploration of underwater sensor networks for marine studies has developed. Network channels for underwater sensor network (USN) rapidly change (spatially and temporally) depending on the surroundings. To increase system efficiency by adjusting transmission parameters to channel fluctuations, it is alluring to utilize adaptive modulation and coding (AMC) for USNs. In order to determine the best link adaptation method based on the channel quality, this article focuses on evaluating a measured sea trial dataset utilizing a rule-based approach (i.e., three-dimensional evaluation, modulation-wise analysis, and a fixed-SNR strategy). To determine the optimum AMC combinations in terms of channel adaptively, we draw a situation of the measured USN data rate versus Bit Error Rate (BER) and Signal to Noise Ratio (SNR). The work further extends to apply machine learning (ML) methods to identify the MCS levels by looking into the channel characteristics due to the non-reversibility limitation of the rule-based strategy. One of the ML methods we used for the investigation, gradient boosted regression tree (GBRT), exhibits impressive accuracy of 99.988% in classifying MCS levels. The MCS levels are related to channel statistics and signal characteristics, particularly those that are susceptible to SNR and BER limitations, using an ensemble of trees that learns from the buoy and base station’s uplink data.
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Gong, Wei, Haoxiang Liu, Jiangchuan Liu, Xiaoyi Fan, Kebin Liu, Qiang Ma et Xiaoyu Ji. « Channel-Aware Rate Adaptation for Backscatter Networks ». IEEE/ACM Transactions on Networking 26, no 2 (avril 2018) : 751–64. http://dx.doi.org/10.1109/tnet.2018.2802323.
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Tridenski, Sergey, et Ram Zamir. « Channel Input Adaptation via Natural Type Selection ». IEEE Transactions on Information Theory 66, no 4 (avril 2020) : 2078–90. http://dx.doi.org/10.1109/tit.2019.2941930.
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Lin, Min, Jeff T. Hatcher, Qin-Hui Chen, Robert D. Wurster et Zixi (Jack) Cheng. « Small conductance Ca2+-activated K+ channels regulate firing properties and excitability in parasympathetic cardiac motoneurons in the nucleus ambiguus ». American Journal of Physiology-Cell Physiology 299, no 6 (décembre 2010) : C1285—C1298. http://dx.doi.org/10.1152/ajpcell.00134.2010.
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Small conductance Ca2+-activated K+ channels (SK) regulate action potential (AP) firing properties and excitability in many central neurons. However, the functional roles of SK channels of parasympathetic cardiac motoneurons (PCMNs) in the nucleus ambiguus have not yet been well characterized. In this study, the tracer X-rhodamine-5 (and 6)-isothiocyanate (XRITC) was injected into the pericardial sac to retrogradely label PCMNs in FVB mice at postnatal days 7–9. Two days later, XRITC-labeled PCMNs in brain stem slices were identified. With the use of whole cell current clamp, single APs and spike trains of different frequencies were evoked by current injections. We found that 1) PCMNs have two different firing patterns: the majority of PCMNs (90%) exhibited spike frequency adaptation (SFA) and the rest (10%) showed less or no adaptation; 2) application of the specific SK channel blocker apamin significantly increased spike half-width in single APs and trains and reduced the spike frequency-dependent AP broadening in trains; 3) SK channel blockade suppressed afterhyperpolarization (AHP) amplitude following single APs and trains and abolished spike-frequency dependence of AHP in trains; and 4) SK channel blockade increased the spike frequency but did not alter the pattern of SFA. Using whole cell voltage clamp, we measured outward currents and afterhyperpolarization current ( IAHP). SK channel blockade revealed that SK-mediated outward currents had both transient and persistent components. After bath application of apamin and Ca2+-free solution, we found that apamin-sensitive and Ca2+-sensitive IAHP were comparable, confirming that SK channels may contribute to a major portion of Ca2+-activated K+ channel-mediated IAHP. These results suggest that PCMNs have SK channels that significantly regulate AP repolarization, AHP, and spike frequency but do not affect SFA. We conclude that activation of SK channels underlies one of the mechanisms for negative control of PCMN excitability.
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Suseendran, G., et E. Chandrasekaran. « Channel Aware MAC Protocol with Rate Adaptation for MANET ». Asian Journal of Science and Applied Technology 2, no 1 (22 avril 2021) : 13–19. http://dx.doi.org/10.51983/ajsat-2013.2.1.754.
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In Mobile Adhoc networks there will be a transient nature of channel conditions. Rate control is the process of switching data rates dynamically based on channel conditions. We propose a rate adaption algorithm. The channel condition information is given as the input to the Rate selection algorithm. Now with the channel condition information, each node uses the rate selection algorithm to calculate the most energy-efficient setting of PHY rates for all links in its maximum interference range.
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Lee, Hyunjee, Haseong Kim et Hosung Park. « Novel Calibration of MIESM and Reduction of CQI Feedback for Improved Fast Link Adaptation ». Electronics 8, no 3 (2 mars 2019) : 278. http://dx.doi.org/10.3390/electronics8030278.
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In mobile communications systems, fast link adaptation (FLA) aims to achieve high system throughput of each user by accurately determining a channel quality indicator (CQI) for feedback, which predicts the next channel based on the current channel state information. In this paper, we propose an improved calibration method of mutual information effective signal-to noise-ratio mapping (MIESM) to determine an accurate CQI feedback value in FLA. Our proposed calibration method derives the optimal calibration factors by considering various channel environments and setting the effective interval of effective signal-to-noise ratio, which is a single value compressing the information of channel characteristics at a time. The simulation is performed in various signal-to-noise ratio (SNR) ranges to account for the actual environments, and the calibration factors are derived from the proposed calibration method. The results show that the CQI feedback value from the derived calibration factors are more accurate than the existing calibration factors. In addition, we discuss a study regarding the time-coherence-based CQI feedback bit reduction scheme. Assuming that each channel is correlated to the previous and subsequent channels, we propose a method to reduce the number of CQI feedback bits adapted to the corresponding SNR regime. Through the simulation, we compare the system throughputs of the proposed adaptive CQI feedback and the conventional CQI feedback scheme. As a result, the proposed CQI feedback has almost the same system throughput as the conventional CQI feedback scheme, but the average number of feedback bits is reduced, thereby improving the efficiency of the communication.
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TOPBAŞ, Benan. « ADAPTATION OF TRADITIONAL MEDIA ORGANS IN VIDEO CONTENT : NEW MEDIA EXAMPLE : CNN TÜRK ». TURKISH ONLINE JOURNAL OF DESIGN ART AND COMMUNICATION 11, no 2 (1 avril 2021) : 393–402. http://dx.doi.org/10.7456/11102100/005.
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The way these main media organs are included in new media outlets, video journalism has been examined. For this purpose, content analysis of the videos produced on cnnturk.com.tr Youtube and social media platforms, which have both traditional and new media organs, was performed. An institutionalized interview was conducted to make the content analysis results more meaningful. In the research, the social media planning of online news videos was examined and what kind of content they had was revealed. Research On cnnturk.com.tr, online news videos are from the pool of CNN TÜRK channel and from agencies, and the channels where readers and viewers react the most are Youtube and Facebook. The site cnnturk.com.tr, a new media organ, shared the online news videos broadcast from the CNN TÜRK channel, which is the traditional media organ, on platforms such as Twitter, Youtube and Facebook, and enabled the videos active in the traditional media to adapt to new media channels.
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Ovchinnikov, Andrei A., et Anna A. Fominykh. « Analysis and optimization of error-correcting coding schemes for channels with Rayleigh fading ». H&ES Research 15, no 3 (2023) : 47–56. http://dx.doi.org/10.36724/2409-5419-2023-15-3-47-56.
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Conventional approach to perform error-correcting decoding in channels with memory is an adoption of interleaving, which increases the receiver complexity and delay. In order to avoid these limitations, approaches for adapting an error-correcting scheme for memory channels may be used. One approach is to use error-correcting codes with modified design and decoding procedure, taking into account the presence of error bursts in the channel. Another approach to adapting the coding scheme for burst error correction is to use product codes with iterative decoding algorithms. Component codes of product codes themselves may not be able to correct error bursts, but a two-dimensional structure of product codes operating as an artificial interleaver and iterative decoding allow for correction of grouping errors. Purpose: The purpose of the study is to analyze the methods of error-correcting code adaptation to burst error correction in channels with memory in order to reduce the probability of error. Results: The study considered methods of error-correcting code scheme adaptation for low-density parity-check codes, polar codes, and product codes for burst error correction in Gilbert-Elliott channel (GE) and correlated Rayleigh fading channel with different correlation coefficients. Degree distribution of low-density parity-check code was optimized for GE channel. The influence of selected parameters of product code component codes on burst error correction in the GE channel was analyzed. The structure of the polar code has been optimized using a genetic algorithm for the correlated Rayleigh channel, which outperforms the 5G polar code design in terms of error probability. Discussion: Existing error-correcting code schemes do not provide theoretically possible limits, so the question remains of developing coding and decoding schemes capable of reaching theoretical limits.
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Nahar, Raufun, Shogo Miwa et Atsuhiko Kai. « Domain Adaptation with Augmented Data by Deep Neural Network Based Method Using Re-Recorded Speech for Automatic Speech Recognition in Real Environment ». Sensors 22, no 24 (16 décembre 2022) : 9945. http://dx.doi.org/10.3390/s22249945.
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The most effective automatic speech recognition (ASR) approaches are based on artificial neural networks (ANN). ANNs need to be trained with an adequate amount of matched conditioned data. Therefore, performing training adaptation of an ASR model using augmented data of matched condition as the real environment gives better results for real data. Real-world speech recordings can vary in different acoustic aspects depending on the recording channels and environment such as the Long Term Evolution (LTE) channel of mobile telephones, where data are transmitted with voice over LTE (VoLTE) technology, wireless pin mics in a classroom condition, etc. Acquiring data with such variation is costly. Therefore, we propose training ASR models with simulated augmented data and fine-tune them for domain adaptation using deep neural network (DNN)-based simulated data along with re-recorded data. DNN-based feature transformation creates realistic speech features from recordings of clean conditions. In this research, a comparative investigation is performed for different recording channel adaptation methods for real-world speech recognition. The proposed method yields 27.0% character error rate reduction (CERR) for the DNN–hidden Markov model (DNN-HMM) hybrid ASR approach and 36.4% CERR for the end-to-end ASR approach for the target domain of the LTE channel of telephone speech.
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Radaydeh, Redha M. « On Power-Efficient Low-Complexity Adaptation for D2D Resource Allocation with Interference Cancelation ». Sensors 23, no 16 (12 août 2023) : 7138. http://dx.doi.org/10.3390/s23167138.
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This paper presents a detailed framework for adaptive low-complexity and power-efficient resource allocation in decentralized device-to-device (D2D) networks. The adopted system model considers that active devices can directly communicate via specified signaling channels. Each D2D receiver attempts to allocate its D2D resources by selecting a D2D transmitter and one of its spectral channels that can meet its performance target. The process is performed adaptively over successive packet durations with the objective of limiting the transmit power on D2D links while reducing the processing complexity. The proposed D2D link adaptation scheme is modeled and analyzed under generalized channel conditions. It considers the random impact of potential D2D transmitters as well as the random number of co-channel interference sources on each D2D link. Interference cancelation schemes are also addressed to alleviate co-channel interference, which can ease the D2D resource allocation process. Generalized formulations for the statistics of the resulting signal-to-interference plus noise ratio (SINR) of the proposed adaptation scheme are presented. Moreover, generic analytical results were developed for some important performance measures as well as processing load measures. They facilitate tradeoff studies between the achieved performance and the processing complexity of the proposed scheme. Insightful results for the distributions of SINRs on individual D2D links under specific fading models are shown in this paper. The results herein add enhancements to some previous contributions and can handle various practical constraints.
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Stefanovic, Mihajlo, Stefan Panic, Jelena Anastasov, Aleksandra Cvetkovic et Zoran Popovic. « Capacity evaluation for maximal ratio combining over κ-μ fading channels ». Serbian Journal of Electrical Engineering 8, no 2 (2011) : 221–28. http://dx.doi.org/10.2298/sjee1102221s.
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Analysis of channel capacity per unit bandwidth of L - branch maximal ratio combining (MRC) receiver operating over ?-? fading channels for two adaptive transmission schemes is presented in this paper. Using the proposed system model, the optimal power and rate adaptation and constant transmit power policies are analyzed. New expressions for capacity evaluation are derived in terms of finite sums. The effects of diversity order and fading parameters on the channel capacity for given techniques have been considered and numerically presented.
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Karger, Amy B., Sungjo Park, Santiago Reyes, Martin Bienengraeber, Roy B. Dyer, Andre Terzic et Alexey E. Alekseev. « Role for SUR2A ED Domain in Allosteric Coupling within the KATP Channel Complex ». Journal of General Physiology 131, no 3 (25 février 2008) : 185–96. http://dx.doi.org/10.1085/jgp.200709852.
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Allosteric regulation of heteromultimeric ATP-sensitive potassium (KATP) channels is unique among protein systems as it implies transmission of ligand-induced structural adaptation at the regulatory SUR subunit, a member of ATP-binding cassette ABCC family, to the distinct pore-forming K+ (Kir6.x) channel module. Cooperative interaction between nucleotide binding domains (NBDs) of SUR is a prerequisite for KATP channel gating, yet pathways of allosteric intersubunit communication remain uncertain. Here, we analyzed the role of the ED domain, a stretch of 15 negatively charged aspartate/glutamate amino acid residues (948–962) of the SUR2A isoform, in the regulation of cardiac KATP channels. Disruption of the ED domain impeded cooperative NBDs interaction and interrupted the regulation of KATP channel complexes by MgADP, potassium channel openers, and sulfonylurea drugs. Thus, the ED domain is a structural component of the allosteric pathway within the KATP channel complex integrating transduction of diverse nucleotide-dependent states in the regulatory SUR subunit to the open/closed states of the K+-conducting channel pore.
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KOBRAVI, A., et M. SHIKH-BAHAEI. « Power and Rate Adaptation Based on Imperfect Channel Estimation over MIMO Fading Channels ». IEICE Transactions on Communications E91-B, no 4 (1 avril 2008) : 1063–67. http://dx.doi.org/10.1093/ietcom/e91-b.4.1063.
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Teng, Zi, Jun Wu, Min Wang et Lifeng Su. « Distributed Coding Modulation Adaptation Scheme for Relay Channel ». Communications and Network 05, no 03 (2013) : 36–41. http://dx.doi.org/10.4236/cn.2013.53b2008.
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Monteiro, Victor Farias, Icaro L. da Silva et Fco Rodrigo P. Cavalcanti. « 5G Measurement Adaptation Based on Channel Hardening Occurrence ». IEEE Communications Letters 23, no 9 (septembre 2019) : 1598–602. http://dx.doi.org/10.1109/lcomm.2019.2926268.
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Kuriki, I. « Multiple-channel characteristics from chromatic notched-noise adaptation ». Journal of Vision 5, no 8 (16 mars 2010) : 266. http://dx.doi.org/10.1167/5.8.266.
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Avinash, Mohan, et Hari K.V.S. « Low complexity adaptation for SISO channel shortening equalizers ». AEU - International Journal of Electronics and Communications 66, no 8 (août 2012) : 600–604. http://dx.doi.org/10.1016/j.aeue.2012.03.011.
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Lesage, Florian, et Jacques Barhanin. « Molecular Physiology of pH-Sensitive Background K2P Channels ». Physiology 26, no 6 (décembre 2011) : 424–37. http://dx.doi.org/10.1152/physiol.00029.2011.
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Background K2P channels are tightly regulated by different stimuli including variations of external and internal pH. pH sensitivity relies on proton-sensing residues that influence channel gating and activity. Gene inactivation in the mouse is a revealing implication of K2P channels in many physiological functions ranging from hormone secretion to central respiratory adaptation. Surprisingly, only a few phenotypic traits of these mice have yet been directly related to the pH sensitivity of K2P channels.
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Pokamestov, Dmitriy, Yakov Kryukov, Eugeniy Rogozhnikov, Islam Kanatbekuli et Edgar Dmitriyev. « SCMA-MIMO system with adaptation to the channel state ». Journal of Physics : Conference Series 2134, no 1 (1 décembre 2021) : 012025. http://dx.doi.org/10.1088/1742-6596/2134/1/012025.
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Abstract Sparse code multiple access (SCMA) is one of the promising implementations of non-orthogonal multiple access (NOMA) methods. SCMA provides high spectral efficiency and a large number of network resources. We describe a communication system with SCMA, space-time block coding (STBC), multiple input multiple output (MIMO) technology, and orthogonal frequency division multiplexing (OFDM). The architecture of such systems, including algorithms of formation and processing of signals is considered. A method for adapting signals to the state of the spatial channel transmission based on information about the matrix of channel coefficients is proposed. The application of such adaptation allows to compensate the influence of the channel and to reduce the probability of bit errors. We consider the bit error rate (BER) performance of the communication system in different channel models and show the effectiveness of the proposed methods.
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Frindt, Gustavo, Hao Zhou, Henry Sackin et Lawrence G. Palmer. « Dissociation of K channel density and ROMK mRNA in rat cortical collecting tubule during K adaptation ». American Journal of Physiology-Renal Physiology 274, no 3 (1 mars 1998) : F525—F531. http://dx.doi.org/10.1152/ajprenal.1998.274.3.f525.
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The density of conducting K channels in the apical membrane of the rat cortical collecting tubule (CCT) is increased by a high-K diet. To see whether this involved increased abundance of mRNA coding for K channel protein, we measured the relative amounts of mRNA for ROMK, the clone of the gene thought to encode the secretory K channel in the CCT. Tubules were isolated and fixed for in situ hybridization with a probe based on the ROMK sequence. Radiolabeled probe associated with the tubule was quantified using densitometric analysis of the autoradiographic images of the tubules. The densitometry signal was shown to be proportional to the amount of radioactive probe in the sample and to the time of exposure of the film. The technique was able to detect an approximately twofold increase in the abundance of mRNA coding for the water channel aquaporin 3 (AQP3), in response to a 30-h dehydration period. Tubules from rats fed a normal diet or a high-K (10% KCl) diet had equal amounts of ROMK mRNA. This suggests that an increase in the abundance of mRNA does not underlie the increase in channel density observed under these conditions.
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Hassinen, Minna, Salla Laulaja, Vesa Paajanen, Jaakko Haverinen et Matti Vornanen. « Thermal adaptation of the crucian carp (Carassius carassius) cardiac delayed rectifier current, IKs, by homomeric assembly of Kv7.1 subunits without MinK ». American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 301, no 1 (juillet 2011) : R255—R265. http://dx.doi.org/10.1152/ajpregu.00067.2011.
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Ectothermic vertebrates experience acute and chronic temperature changes which affect cardiac excitability and may threaten electrical stability of the heart. Nevertheless, ectothermic hearts function over wide range of temperatures without cardiac arrhythmias, probably due to special molecular adaptations. We examine function and molecular basis of the slow delayed rectifier K+ current ( IKs) in cardiac myocytes of a eurythermic fish ( Carassius carassius L.). IKs is an important repolarizing current that prevents excessive prolongation of cardiac action potential, but it is extremely slowly activating when expressed in typical molecular composition of the endothermic animals. Comparison of the IKs of the crucian carp atrial myocytes with the currents produced by homomeric Kv7.1 and heteromeric Kv7.1/MinK channels in Chinese hamster ovary cells indicates that activation kinetics and pharmacological properties of the IKs are similar to those of the homomeric Kv7.1 channels. Consistently with electrophysiological properties and homomeric Kv7.1 channel composition, atrial transcript expression of the MinK subunit is only 1.6–1.9% of the expression level of the Kv7.1 subunit. Since activation kinetics of the homomeric Kv7.1 channels is much faster than activation of the heteromeric Kv7.1/MinK channels, the homomeric Kv7.1 composition of the crucian carp cardiac IKs is thermally adaptive: the slow delayed rectifier channels can open despite low body temperatures and curtail the duration of cardiac action potential in ectothermic crucian carp. We suggest that the homomeric Kv7.1 channel assembly is an evolutionary thermal adaptation of ectothermic hearts and the heteromeric Kv7.1/MinK channels evolved later to adapt IKs to high body temperature of endotherms.
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Liang, Shuang, Yu-Shuang Sun, Lu Li, Yao Long, Meng Wang, Hou-Zhi Yang, Chun-Di Li et al. « Progesterone Changes the Pregnancy-Induced Adaptation of Cardiomyocyte Kv2.1 Channels via MicroRNA-29b ». Cardiovascular Therapeutics 2022 (7 avril 2022) : 1–19. http://dx.doi.org/10.1155/2022/7145699.
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The cardiovascular system adaptation occurs during pregnancy to ensure adequate maternal circulation. Progesterone (P4) is widely used in hormone therapy to support pregnancy, but little is known about its effects on maternal cardiac function. In this study, we investigated the cardiac repolarization and ion channel expression in pregnant subjects and mice models and studied the effects of P4 administrations on these pregnancy-mediated adaptations. P4 administrations shortened the prolongation of QTC intervals and action potential duration (APD) that occurred during pregnancy, which was mainly attributable to the reduction in the voltage-gated potassium (Kv) current under basal conditions. In vitro studies indicated that P4 regulated the Kv2.1 channel in a bidirectional manner. At a low dose (1 μM), P4 induced upregulation of Kv2.1 through P4 receptor, while at a higher dose (5 μM), P4 downregulated Kv2.1 by targeting microRNA-29b (miR-29b). Our data showed that P4 modulated maternal cardiac repolarization by regulating Kv2.1 channel activity during pregnancy. Kv2.1, as well as miR-29b, might be used as potential therapeutic targets for adaptations of the maternal cardiovascular system or evaluation of progesterone medication during pregnancy.
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Hamill, OP, et DW, McBride. « Molecular Mechanisms of Mechanoreceptor Adaptation ». Physiology 9, no 2 (1 avril 1994) : 53–59. http://dx.doi.org/10.1152/physiologyonline.1994.9.2.53.
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Mechanoreceptor adaptation to maintained stimulation serves to maximize dynamic sensitivity over a broad stimulus domain. Mechanosensitive channel currents in hair cells and oocytes show similar voltage-dependent adaptation. However, in the hair cell, adaptation appears dependent on Ca2+ influx, whereas in the oocyte, it is intrinsically voltage sensitive.
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Xie, Man-Jiang, Yu-Guang Ma, Fang Gao, Yun-Gang Bai, Jiu-Hua Cheng, Yao-Ming Chang, Zhi-Bin Yu et Jin Ma. « Activation of BKCa channel is associated with increased apoptosis of cerebrovascular smooth muscle cells in simulated microgravity rats ». American Journal of Physiology-Cell Physiology 298, no 6 (juin 2010) : C1489—C1500. http://dx.doi.org/10.1152/ajpcell.00474.2009.
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Cerebral arterial remodeling is one of the critical factors in the occurrence of postspaceflight orthostatic intolerance. We hypothesize that large-conductance calcium-activated K+ (BKCa) channels in vascular smooth muscle cells (VSMCs) may play an important role in regulating cerebrovascular adaptation during microgravity exposure. The aim of this work was to investigate whether activation of BKCa channels is involved in regulation of apoptotic remodeling of cerebral arteries in simulated microgravity rats. In animal studies, Sprague-Dawley rats were subjected to 1-wk hindlimb unweighting to simulate microgravity. Alterations of BKCa channels in cerebral VSMCs were investigated by patch clamp and Western blotting; apoptosis was assessed by electron microscopy and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick-end labeling (TUNEL). To evaluate the correlation of BKCa channel and apoptosis, channel protein and cell nucleus were double-stained. In cell studies, hSloα+β1 channel was coexpressed into human embryonic kidney 293 (HEK293) cells to observe the effects of BKCa channels on apoptosis. In rats, enhanced activities and expression of BKCa channels were found to be correlated with increased apoptosis in cerebral VSMCs after simulated microgravity. In transfected HEK293 cells, activation of cloned BKCa channel induced apoptosis, whereas inhibition of cloned BKCa channel decreased apoptosis. In conclusion, activation of BKCa channels is associated with increased apoptosis in cerebral VSMCs of simulated microgravity rats.
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Wei, Yuan, Yi Liao, Beth Zavilowitz, Jin Ren, Wen Liu, Pokman Chan, Rajeev Rohatgi et al. « Angiotensin II type 2 receptor regulates ROMK-like K+ channel activity in the renal cortical collecting duct during high dietary K+ adaptation ». American Journal of Physiology-Renal Physiology 307, no 7 (1 octobre 2014) : F833—F843. http://dx.doi.org/10.1152/ajprenal.00141.2014.
Texte intégralRésumé :
The kidney adjusts K+ excretion to match intake in part by regulation of the activity of apical K+ secretory channels, including renal outer medullary K+ (ROMK)-like K+ channels, in the cortical collecting duct (CCD). ANG II inhibits ROMK channels via the ANG II type 1 receptor (AT1R) during dietary K+ restriction. Because AT1Rs and ANG II type 2 receptors (AT2Rs) generally function in an antagonistic manner, we sought to characterize the regulation of ROMK channels by the AT2R. Patch-clamp experiments revealed that ANG II increased ROMK channel activity in CCDs isolated from high-K+ (HK)-fed but not normal K+ (NK)-fed rats. This response was blocked by PD-123319, an AT2R antagonist, but not by losartan, an AT1R antagonist, and was mimicked by the AT2R agonist CGP-42112. Nitric oxide (NO) synthase is present in CCD cells that express ROMK channels. Blockade of NO synthase with N-nitro-l-arginine methyl ester and free NO with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt completely abolished ANG II-stimulated ROMK channel activity. NO enhances the synthesis of cGMP, which inhibits phosphodiesterases (PDEs) that normally degrade cAMP; cAMP increases ROMK channel activity. Pretreatment of CCDs with IBMX, a broad-spectrum PDE inhibitor, or cilostamide, a PDE3 inhibitor, abolished the stimulatory effect of ANG II on ROMK channels. Furthermore, PKA inhibitor peptide, but not an activator of the exchange protein directly activated by cAMP (Epac), also prevented the stimulatory effect of ANG II. We conclude that ANG II acts at the AT2R to stimulate ROMK channel activity in CCDs from HK-fed rats, a response opposite to that mediated by the AT1R in dietary K+-restricted animals, via a NO/cGMP pathway linked to a cAMP-PKA pathway.