Science.gov

Sample records for fading nakagami channels

  1. Outage Performance of Cooperative Relay Selection with Multiple Source and Destination Antennas over Dissimilar Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Lee, Wooju; Yoon, Dongweon

    Cooperative relay selection, in which one of multiple relays is selected to retransmit the source signal to the destination, has received considerable attention in recent years, because it is a simple way to obtain cooperative diversity in wireless networks. The exact expression of outage probability for a decode-and-forward cooperative relay selection with multiple source and destination antennas over Rayleigh fading channels was recently derived in [9]. In this letter, we derive the exact expressions of outage probability and diversity-multiplexing tradeoff over independent and non-identically distributed Nakagami-m fading channels as an extension of [9]. We then analyze the effects of various parameters such as fading conditions, number of relays, and number of source and destination antennas on the outage probability.

  2. Bit Error Rate Analysis for MC-CDMA Systems in Nakagami-[InlineEquation not available: see fulltext.] Fading Channels

    NASA Astrophysics Data System (ADS)

    Li, Zexian; Latva-aho, Matti

    2004-12-01

    Multicarrier code division multiple access (MC-CDMA) is a promising technique that combines orthogonal frequency division multiplexing (OFDM) with CDMA. In this paper, based on an alternative expression for the[InlineEquation not available: see fulltext.]-function, characteristic function and Gaussian approximation, we present a new practical technique for determining the bit error rate (BER) of multiuser MC-CDMA systems in frequency-selective Nakagami-[InlineEquation not available: see fulltext.] fading channels. The results are applicable to systems employing coherent demodulation with maximal ratio combining (MRC) or equal gain combining (EGC). The analysis assumes that different subcarriers experience independent fading channels, which are not necessarily identically distributed. The final average BER is expressed in the form of a single finite range integral and an integrand composed of tabulated functions which can be easily computed numerically. The accuracy of the proposed approach is demonstrated with computer simulations.

  3. Moments Of Microdiversity EGC Receivers And Macrodiversity SC Receiver Output Signal Over Gamma Shadowed Nakagami-m Multipath Fading Channel

    NASA Astrophysics Data System (ADS)

    Djordjević, Nebojša; Jaksić, Branimir S.; Matović, Ana; Matović, Marija; Smilić, Marko

    2015-11-01

    A system with macrodiversity selection combining (SC) receiver and for microdiversity equal gain combining (EGC) receivers is considered. Received signal is subjected, simultaneously to multipath fading and shadowing, resulting in signal envelope and signal power variation. Closed form expressions for moments of macrodiversity SC receiver output signal envelope are calculated. Numerical expressions are plotted to present the influences of Gamma shadowing severity and Nakagami-m severity on moments of proposed system output signal.

  4. Fading channel simulator

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.

    1991-12-31

    This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  5. Fading channel simulator

    DOEpatents

    Argo, Paul E.; Fitzgerald, T. Joseph

    1993-01-01

    Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  6. Comparasion of Energy Detection in Cognitive Radio over different fading channels

    NASA Astrophysics Data System (ADS)

    Buttar, Simar

    2012-07-01

    With the advance of wireless communications, the problem of bandwidth scarcity has become more prominent. Cognitive radio technology has come out as a way to solve this problem by allowing the unlicensed users to use the licensed bands opportunistically. To sense the existence of licensed users, many spectrum sensing techniques have been devised. In this paper, energy detection and cyclic prefix is used for spectrum sensing.The comparison of ROC curves has been done for various wireless fading channels using squaring and cubingoperation,the improvement has gone as high as up to 0.6 times for AWGN channel and 0.4 times for Rayleigh channel as we go from squaring to cubing operation in an energy detector. Closed form expressions for Probability of detection for AWGN and Rayleigh channels are described.Nakagami fading channel shows worst results .

  7. Fade margin calculation for channels impaired by Rician fading

    NASA Technical Reports Server (NTRS)

    Davarian, F.

    1985-01-01

    Excess path loss due to multipath severely restricts the performance of power limited mobile networks such as those using satellite-aided links. To reduce multipath related losses, the higher elevation angle of the spacecraft can be exploited by utilizing mobile antennas which reduce the strength of the multipath reflections in favor of the line-of-sight signal. The presence of a strong and stable path in a fading link will change the envelope statistics of the received waveform from Rayleigh to a more favorable Rician distribution. It is determined that the excess path loss, or fade margin, of a Rician channel when coherent detection of binary phase shift keying (BPSK) or quaternary phase shift keying (QPSK) signals is considered. The results are presented parametrically such that they can be applied to a wide range of propagation characteristics from heavy fading to nonfading situations. Furthermore, similar results are also given for the case where only limited coverage is provided.

  8. Bit Error Rate Performance of Partially Coherent Dual-Branch SSC Receiver over Composite Fading Channels

    NASA Astrophysics Data System (ADS)

    Milić, Dejan N.; Đorđević, Goran T.

    2013-01-01

    In this paper, we study the effects of imperfect reference signal recovery on the bit error rate (BER) performance of dual-branch switch and stay combining receiver over Nakagami-m fading/gamma shadowing channels with arbitrary parameters. The average BER of quaternary phase shift keying is evaluated under the assumption that the reference carrier signal is extracted from the received modulated signal. We compute numerical results illustrating simultaneous influence of average signal-to-noise ratio per bit, fading severity, shadowing, phase-locked loop bandwidth-bit duration (BLTb) product, and switching threshold on BER performance. The effects of BLTb on receiver performance under different channel conditions are emphasized. Optimal switching threshold is determined which minimizes BER performance under given channel and receiver parameters.

  9. Detection performance of cooperative spectrum sensing with hard decision fusion in fading channels

    NASA Astrophysics Data System (ADS)

    Nallagonda, S.; Chandra, A.; Roy, S. D.; Kundu, S.; Kukolev, P.; Prokes, A.

    2016-02-01

    In this paper, we investigate the detection performance of cooperative spectrum sensing (CSS) using energy detector in several fading scenarios. The fading environments comprise relatively less-studied Hoyt and Weibull channels in addition to the conventional Rayleigh, Rician, Nakagami-m and log-normal shadowing channels. We have presented an analytical framework for evaluating different probabilities related to spectrum sensing, i.e. missed detection, false alarm and total error due to both of them, for all the fading/shadowing models mentioned. The major theoretical contribution is, however, the derivation of closed-form expressions for probability of detection. Based on our developed framework, we present performance results of CSS under various hard decision fusion strategies such as OR rule, AND rule and Majority rule. Effects of sensing channel signal-to-noise ratio, detection threshold, fusion rules, number of cooperating cognitive radios (CRs) and fading/shadowing parameters on the sensing performance have been illustrated. The performance improvement achieved with CSS over a single CR-based sensing is depicted in terms of total error probability. Further, an optimal threshold that minimises total error probability has been indicated for all the fading/shadowing channels.

  10. Wireless Fading Channel Models: From Classical to Stochastic Differential Equations

    SciTech Connect

    Olama, Mohammed M; Djouadi, Seddik M; Charalambous, Prof. Charalambos

    2010-01-01

    expanded to three-dimensions (3D) by Aulin. An indoor STF was introduced. Most of these STF models provide information on the frequency response of the channel, described by the Doppler power spectral density (DPSD). Aulin presented a methodology to find the Doppler power spectrum by computing the Fourier transform of the autocorrelation function of the channel impulse response with respect to time. A different approach, leading to the same Doppler power spectrum relation was presented by Gans. These STF models suggest various distributions for the received signal amplitude such as Rayleigh, Rician, or Nakagami. Models based on autoregressive and moving averages (AR) are proposed. However, these models assume that the channel state is completely observable, which in reality is not the case due to additive noise, and requires long observation intervals. First order Markov models for Raleigh fading have been proposed, and the usefulness of a finite-state Markov channel model is argued. Mobile-to-mobile (or ad hoc) wireless networks comprise nodes that freely and dynamically self-organize into arbitrary and/or temporary network topology without any fixed infrastructure support. They require direct communication between a mobile transmitter and a mobile receiver over a wireless medium. Such mobile-to-mobile communication systems differ from the conventional cellular systems, where one terminal, the base station, is stationary, and only the mobile station is moving. As a consequence, the statistical properties of mobile-to-mobile links are different from cellular ones. Copious ad hoc networking research exists on layers in the open system interconnection (OSI) model above the physical layer. However, neglecting the physical layer while modeling wireless environment is error prone and should be considered more carefully. The experimental results show that the factors at the physical layer not only affect the absolute performance of a protocol, but because their impact on

  11. Performance Characterization of a Hybrid Satellite-Terrestrial System with Co-Channel Interference over Generalized Fading Channels.

    PubMed

    Javed, Umer; He, Di; Liu, Peilin

    2016-08-05

    The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes.

  12. Performance Characterization of a Hybrid Satellite-Terrestrial System with Co-Channel Interference over Generalized Fading Channels

    PubMed Central

    Javed, Umer; He, Di; Liu, Peilin

    2016-01-01

    The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes. PMID:27527182

  13. Performance Characterization of a Hybrid Satellite-Terrestrial System with Co-Channel Interference over Generalized Fading Channels.

    PubMed

    Javed, Umer; He, Di; Liu, Peilin

    2016-01-01

    The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes. PMID:27527182

  14. Trellis coded modulation for transmission over fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K. (Inventor); Divasalar, Dariush (Inventor)

    1990-01-01

    The combination of trellis coding and multiple phase-shift keyed (MPSK) signaling with asymmetry (nonuniform spacing) to the signal set is disclosed with regard to its suitability for a fading mobile satellite communication channel. For MPSK signaling, introducing nonuniformity in the phase spacing between signal points provides an improvement in performance over that achievable with trellis codes symmetric MPSK signaling, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Block interleaving may be used to reduce error and pilot tone(s) may be used for improving the error correction performance of the trellis decoder in the presence of channel fading.

  15. The design of trellis codes for fading channels

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Simon, Marvin K.

    1987-01-01

    The appropriate criterion for optimum trellis coded modulation design on the additive white Gaussian noise channel is maximization of the free Euclidean distance. When trellis coded modulation is used on a Rician fading channel with interleaving/deinterleaving, the design of the code for optimum performance is guided by other factors, in particular the length of the shortest error event path, and the product of branch distances (possibly normalized by the Euclidean distance of the path) along that path. Although maximum free distance (d sub free) is still an important consideration, it plays a less significant role the more severe the fading is on the channel. These considerations lead to the definition of a new distance measure for optimization of trellis codes transmitted over Rician fading channels. If no interleaving/deinterleaving is used, then once again the design of the trellis code is guided by maximizing d sub free. It is also shown that allowing for multiple symbols per trellis branch, i.e., multiple trellis coded modulation (MTCM), provides an additional degree of freedom for designing a code to meet the above optimization criteria on the fading channel. It is here where the MTCM technique exploits its full potential.

  16. Optimal Performance Monitoring of Hybrid Mid-Infrared Wavelength MIMO Free Space Optical and RF Wireless Networks in Fading Channels

    NASA Astrophysics Data System (ADS)

    Schmidt, Barnet Michael

    An optimal performance monitoring metric for a hybrid free space optical and radio-frequency (RF) wireless network, the Outage Capacity Objective Function, is analytically developed and studied. Current and traditional methods of performance monitoring of both optical and RF wireless networks are centered on measurement of physical layer parameters, the most common being signal-to-noise ratio, error rate, Q factor, and eye diagrams, occasionally combined with link-layer measurements such as data throughput, retransmission rate, and/or lost packet rate. Network management systems frequently attempt to predict or forestall network failures by observing degradations of these parameters and to attempt mitigation (such as offloading traffic, increasing transmitter power, reducing the data rate, or combinations thereof) prior to the failure. These methods are limited by the frequent low sensitivity of the physical layer parameters to the atmospheric optical conditions (measured by optical signal-to-noise ratio) and the radio frequency fading channel conditions (measured by signal-to-interference ratio). As a result of low sensitivity, measurements of this type frequently are unable to predict impending failures sufficiently in advance for the network management system to take corrective action prior to the failure. We derive and apply an optimal measure of hybrid network performance based on the outage capacity of the hybrid optical and RF channel, the outage capacity objective function. The objective function provides high sensitivity and reliable failure prediction, and considers both the effects of atmospheric optical impairments on the performance of the free space optical segment as well as the effect of RF channel impairments on the radio frequency segment. The radio frequency segment analysis considers the three most common RF channel fading statistics: Rayleigh, Ricean, and Nakagami-m. The novel application of information theory to the underlying physics of the

  17. Multi-dimensional modulation codes for fading channel

    NASA Technical Reports Server (NTRS)

    Lin, Shu; Wu, Jiantian

    1991-01-01

    Some new codes are presented which have good performance on Rician fading channel with small decoding complexities. A new M-way partition chain is proposed for the L x MPSK (L less than or equal to M) signal set which maximizes the intra-set distance of each subset at each partition level. Based on this partition chain, a class of asymptotical optimum codes was found. For M = 4, these codes have both large symbol distances and product distances. Multi-level coding scheme allows to construct a code by hand such that the code meets some desired parameters, e.g., symbol distance, product distance, etc. In design of a multi-level code, all factors were considered which affect the performance and complexity of the code, such as, the decoding scheme, decoding complexity, and performance under the decoding scheme, e.g., if the multi-stage decoding scheme is used, the performance degradation due to the suboptimum decoding is taken into consideration. The performance for most of the presented codes was simulated on Rayleigh fading channel, and the results show that these codes have good performance with small decoding complexities.

  18. Multicarrier chaotic communications in multipath fading channels without channel estimation

    SciTech Connect

    Wang, Shilian Zhang, Zhili

    2015-01-15

    A multi-carrier chaotic shift keying(MC-CSK) communication scheme with low probability of interception(LPI) is proposed in this article. We apply chaotic spreading sequences in the frequency domain, mapping a different chip of a chaotic sequence to an individual orthogonal frequency division multiplexing(OFDM) subcarrier. In each block size of $M$ OFDM symbols, we use one pilot OFDM symbol inserted time-spaced in all-frequency to transmit the reference chaotic signal and use the other M-1 OFDM symbols to transmit the information-bearing signals each spreaded by the reference chaotic signal. At the receiver, we construct a differential detector after DFT and recover the information bits from the correlations between the pilot OFDM symbol and the other M-1 OFDM symbols in each block size of M. Performance analysis and computer simulations show that the MC-CSK outperforms differential chaos shift keying(DCSK) in AWGN channels with high bandwidth efficiency for the block size of M=2 and that the MC-CSK exploits effectively the frequent diversity of the multipath channel.

  19. Separable concatenated codes with iterative map decoding for Rician fading channels

    NASA Astrophysics Data System (ADS)

    Lodge, J. H.; Young, R. J.

    Very efficient signalling in radio channels requires the design of very powerful codes having special structure suitable for practical decoding schemes. In this paper, powerful codes are obtained by combining comparatively simple convolutional codes to form multi-tiered 'separable' convolutional codes. The decoding of these codes, using separable symbol-by-symbol maximum a posteriori (MAP) 'filters', is described. It is known that this approach yields impressive results in non-fading additive white Gaussian noise channels. Interleaving is an inherent part of the code construction, and consequently, these codes are well suited for fading channel communications. Here, simulation results for communications over Rician fading channels are presented to support this claim.

  20. Separable concatenated codes with iterative map decoding for Rician fading channels

    NASA Technical Reports Server (NTRS)

    Lodge, J. H.; Young, R. J.

    1993-01-01

    Very efficient signalling in radio channels requires the design of very powerful codes having special structure suitable for practical decoding schemes. In this paper, powerful codes are obtained by combining comparatively simple convolutional codes to form multi-tiered 'separable' convolutional codes. The decoding of these codes, using separable symbol-by-symbol maximum a posteriori (MAP) 'filters', is described. It is known that this approach yields impressive results in non-fading additive white Gaussian noise channels. Interleaving is an inherent part of the code construction, and consequently, these codes are well suited for fading channel communications. Here, simulation results for communications over Rician fading channels are presented to support this claim.

  1. Estimation of FBMC/OQAM Fading Channels Using Dual Kalman Filters

    PubMed Central

    Aldababseh, Mahmoud

    2014-01-01

    We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method. PMID:24701181

  2. Estimation of FBMC/OQAM fading channels using dual Kalman filters.

    PubMed

    Aldababseh, Mahmoud; Jamoos, Ali

    2014-01-01

    We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method. PMID:24701181

  3. The performance of trellis coded multilevel DPSK on a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K.; Divsalar, Dariush

    1987-01-01

    The performance of trellis coded multilevel differential phase-shift-keying (MDPSK) over Rician and Rayleigh fading channels is discussed. For operation at L-Band, this signalling technique leads to a more robust system than the coherent system with dual pilot tone calibration previously proposed for UHF. The results are obtained using a combination of analysis and simulation. The analysis shows that the design criterion for trellis codes to be operated on fading channels with interleaving/deinterleaving is no longer free Euclidean distance. The correct design criterion for optimizing bit error probability of trellis coded MDPSK over fading channels will be presented along with examples illustrating its application.

  4. A tone-aided dual vestigial sideband system for digital communications on fading channels

    NASA Technical Reports Server (NTRS)

    Hladik, Stephen M.; Saulnier, Gary J.; Rafferty, William

    1989-01-01

    A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.

  5. On The Phase Crossing Statistics and Random FM Noise in Generalized Rice Fading Channels

    NASA Astrophysics Data System (ADS)

    Petković, Marko D.; Stefanović, Mihajlo Č.

    2012-01-01

    In this paper we consider phase process second order statistics of generalized Rice (Beckmann) multipath fading channel. Closed-form expression for JPDF of phase and random FM noise is derived. Furthermore expressions for the PDF and CDF of random FM noise are obtained. The level-crossing rate of the phase process is then obtained for any phase crossing level. Obtained expressions reduces to known ones for Hoyt, Rice and Rayleigh fading channels, since these are the special cases of generalized Rice fading channel. Moreover, derived analytical expressions are compared with results obtained by computer simulation where excellent agreement is achieved. Presented results can be applied for analyzing the statistics of FM spikes in the case of data transmission over generalized Rice fading channels.

  6. Performance of DPSK with convolutional encoding on time-varying fading channels

    NASA Technical Reports Server (NTRS)

    Mui, S. Y.; Modestino, J. W.

    1977-01-01

    The bit error probability performance of a differentially-coherent phase-shift keyed (DPSK) modem with convolutional encoding and Viterbi decoding on time-varying fading channels is examined. Both the Rician and the lognormal channels are considered. Bit error probability upper bounds on fully-interleaved (zero-memory) fading channels are derived and substantiated by computer simulation. It is shown that the resulting coded system performance is a relatively insensitive function of the choice of channel model provided that the channel parameters are related according to the correspondence developed as part of this paper. Finally, a comparison of DPSK with a number of other modulation strategies is provided.

  7. A novel scheme to aid coherent detection of GMSK signals in fast Rayleigh fading channels

    NASA Technical Reports Server (NTRS)

    Leung, Patrick S. K.; Feher, Kamilo

    1990-01-01

    A novel scheme to insert carrier pilot to Gaussian Minimum Shift Keying (GMSK) signal using Binary Block Code (BBC) and a highpass filter in baseband is proposed. This allows the signal to be coherently demodulated even in a fast Rayleigh fading environment. As an illustrative example, the scheme is applied to a 16 kb/s GMSK signal, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. This modem's 'irreducible error rate' is found to be Pe = 5.5 x 10(exp -5) which is more than that of differential detection. The modem's performance in Rician fading channel is currently under investigation.

  8. Bandwidth efficient coding for fading channels - Code construction and performance analysis

    NASA Technical Reports Server (NTRS)

    Schlegel, Christian; Costello, Daniel J., Jr.

    1989-01-01

    The authors apply a general method of bounding the event error probability of trellis-coded modulation schemes to fading channels and use the effective length and the minimum-squared-product distance to replace the minimum-free-squared-Euclidean distance as code design parameters for Rayleigh and Rician fading channels with a substantial multipath component. They present 8-PSK trellis codes specifically constructed for fading channels that outperform equivalent codes designed for the additive white Gaussian noise channel when v is greater than or equal to 5. For quasiregular trellis codes there exists an efficient algorithm for evaluating event error probability, and numerical results on Pe which demonstrate the importance of the effective length as a code design parameter for fading channels with or without side information have been obtained. This is consistent with the case for binary signaling, where the Hamming distance remains the best code design parameter for fading channels. The authors show that the use of Reed-Solomon block codes with expanded signal sets becomes interesting only for large values of E(s)/N(0), where they begin to outperform trellis codes.

  9. Channel fading for mobile satellite communications using spread spectrum signaling and TDRSS

    NASA Technical Reports Server (NTRS)

    Jenkins, Jeffrey D.; Fan, Yiping; Osborne, William P.

    1995-01-01

    This paper will present some preliminary results from a propagation experiment which employed NASA's TDRSS and an 8 MHz chip rate spread spectrum signal. Channel fade statistics were measured and analyzed in 21 representative geographical locations covering urban/suburban, open plain, and forested areas. Cumulative distribution Functions (CDF's) of 12 individual locations are presented and classified based on location. Representative CDF's from each of these three types of terrain are summarized. These results are discussed, and the fade depths exceeded 10 percent of the time in three types of environments are tabulated. The spread spectrum fade statistics for tree-lined roads are compared with the Empirical Roadside Shadowing Model.

  10. Second order statistics of selection combining receiver over κ-μ fading channels subject to co-channel interferences

    NASA Astrophysics Data System (ADS)

    Stefanović, Mihajlo; Panić, Stefan R.; Stefanović, DušAn; Nikolić, Bojana; Cvetković, Aleksandra

    2012-12-01

    Radio propagation performances in interference-limited faded environment are studied in this paper. Selection combining (SC) based on signal-to-interference ratio (SIR) overκ-μfading channels is performed. Probability density function (PDF) and cumulative distribution function (CDF) of the received SIR are determined. Based on the results obtained for PDF and CDF, infinite-series expressions are derived for the output level crossing rate (LCR) and average fade duration (AFD). These second order statistical measures are regarded as necessary for supporting technical documentation in every radio communication link design. Influences of various system parameters such as fading severity and the number of co-channel interferences affecting these measures are graphically presented and discussed.

  11. Frequency-selective fading statistics of shallow-water acoustic communication channel with a few multipaths

    NASA Astrophysics Data System (ADS)

    Bae, Minja; Park, Jihyun; Kim, Jongju; Xue, Dandan; Park, Kyu-Chil; Yoon, Jong Rak

    2016-07-01

    The bit error rate of an underwater acoustic communication system is related to multipath fading statistics, which determine the signal-to-noise ratio. The amplitude and delay of each path depend on sea surface roughness, propagation medium properties, and source-to-receiver range as a function of frequency. Therefore, received signals will show frequency-dependent fading. A shallow-water acoustic communication channel generally shows a few strong multipaths that interfere with each other and the resulting interference affects the fading statistics model. In this study, frequency-selective fading statistics are modeled on the basis of the phasor representation of the complex path amplitude. The fading statistics distribution is parameterized by the frequency-dependent constructive or destructive interference of multipaths. At a 16 m depth with a muddy bottom, a wave height of 0.2 m, and source-to-receiver ranges of 100 and 400 m, fading statistics tend to show a Rayleigh distribution at a destructive interference frequency, but a Rice distribution at a constructive interference frequency. The theoretical fading statistics well matched the experimental ones.

  12. Trellis coded modulation for 4800-9600 bps transmission over a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Divsalar, D.; Simon, M. K.

    1986-01-01

    The combination of trellis coding and multiple phase-shift-keyed (MPSK) signalling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

  13. Design of a robust underwater acoustic communication system over multipath fading channels

    NASA Astrophysics Data System (ADS)

    Kim, Jangeun; Shim, Taebo

    2012-11-01

    Due to the surface and bottom constraints of the underwater acoustic channel (UAC) in shallow waters, multipath fading occurs and causes degradation of the signal for the UAC system. To overcome these problems, a robust underwater acoustic communication system was designed over multipath fading channels by employing both decision feedback equalization with the RLS algorithm and convolutional coding with interleaving+shuffling block data sequence. The dual use of these two methods simultaneously can reduce the intersymbol interference (ISI) and the adjacent bit and burst errors. The system will retransmit the same signal if the system fails to estimate the channel due to severe multipath fading. To verify the performance of the system, the transmission of an image was tested using a 524,288bit gray-scaled image through the multipath fading channel. The test results showed that the number of bit errors was reduced from 86,824 to 5,106 when the reference SNR was 12 dB.

  14. Receiver diversity combining using evolutionary algorithms in Rayleigh fading channel.

    PubMed

    Akbari, Mohsen; Manesh, Mohsen Riahi; El-Saleh, Ayman A; Reza, Ahmed Wasif

    2014-01-01

    In diversity combining at the receiver, the output signal-to-noise ratio (SNR) is often maximized by using the maximal ratio combining (MRC) provided that the channel is perfectly estimated at the receiver. However, channel estimation is rarely perfect in practice, which results in deteriorating the system performance. In this paper, an imperialistic competitive algorithm (ICA) is proposed and compared with two other evolutionary based algorithms, namely, particle swarm optimization (PSO) and genetic algorithm (GA), for diversity combining of signals travelling across the imperfect channels. The proposed algorithm adjusts the combiner weights of the received signal components in such a way that maximizes the SNR and minimizes the bit error rate (BER). The results indicate that the proposed method eliminates the need of channel estimation and can outperform the conventional diversity combining methods.

  15. Receiver Diversity Combining Using Evolutionary Algorithms in Rayleigh Fading Channel

    PubMed Central

    Akbari, Mohsen; Manesh, Mohsen Riahi

    2014-01-01

    In diversity combining at the receiver, the output signal-to-noise ratio (SNR) is often maximized by using the maximal ratio combining (MRC) provided that the channel is perfectly estimated at the receiver. However, channel estimation is rarely perfect in practice, which results in deteriorating the system performance. In this paper, an imperialistic competitive algorithm (ICA) is proposed and compared with two other evolutionary based algorithms, namely, particle swarm optimization (PSO) and genetic algorithm (GA), for diversity combining of signals travelling across the imperfect channels. The proposed algorithm adjusts the combiner weights of the received signal components in such a way that maximizes the SNR and minimizes the bit error rate (BER). The results indicate that the proposed method eliminates the need of channel estimation and can outperform the conventional diversity combining methods. PMID:25045725

  16. Simulated performance of coded PCM/FM modem on Rician fading channel

    NASA Technical Reports Server (NTRS)

    Modestino, J. W.; Sher, J. S.

    1976-01-01

    This paper describes a simulation approach to characterizing the performance of a coded PCM/FM modem operating on the classical Rician fading channel. In particular, we consider the performance of short constraint length convolutional codes in conjunction with Viterbi maximum likelihood decoding. The receiver consists of a narrowband filter followed by an ideal limiter/discriminator. Primary interest is in the bit error probability performance parameterized by both the fading channel and receiver parameters. Particular attention is given to simulating the impulse noise appearing at the discriminator output. This is the 'click' noise caused by encirclements of the origin by the instantaneous signal-plus-noise phasor. Results include the effects of channel memory and narrowband receiver filtering effects on overall bit error probability.

  17. Robustness of predictive sensor network routing in fading channels

    NASA Astrophysics Data System (ADS)

    Muraleedharan, Rajani; Osadciw, Lisa A.

    2005-06-01

    Sensors have varied constraints, which make the network challenging for communicating with peers. In this paper, an extension, to the physical layer of the previous predictive sensor network model using the ant system is proposed. The tiny and low-cost sensor nodes are made of RF wireless links, where the states of the nodes vary with respect to time and environment. The ant system is a learning algorithm, that can be used to solve any NP hard communication problem and possesses characteristics such as robustness and versatility. The ant system possesses unique features that keep the network functional by detecting weak links and re-routing the agents. The swarm agents are distributed along the network, where the agent communicates with its neighbors (agents) by means of pheromone deposition and tabu list. The transition probability in the ant system includes an objective function, which is influenced by the poset weights. The poset weights on each of the orthogonal communication parameters greatly affects the decisions made by ant system. The agents carry updated information of its previous nodes, which helps in monitoring the strength of the communication links. Through simulation, comparison between DSSS-BPSK and Bluetooth-GFSK signals are shown. This paper demonstrates the robustness of the model under slow/fast fading, and energy loss at node during transmission. Implementation of this algorithm should be able to handle hostile environmental conditions and human tampering of data. The performance of the network is evaluated based on accuracy and response time of the agents within the network.

  18. Laboratory measurements and a theoretical analysis of the TCT fading channel radio system. [Tone Calibrated Technique

    NASA Technical Reports Server (NTRS)

    Rafferty, William; Anderson, John B.; Saulnier, Gary J.; Holm, John R.

    1987-01-01

    This paper documents the laboratory and theoretical performance of a pilot-aided digital radio system. The technique considered transmits a midband pilot tone to improve the receiver data detection performance in a multipath fading channel and is referred to as the tone calibrated technique (TCT). The performance of a 860 MHz prototype system carrying 2.4 kbit/s data under Rician fading conditions is reported. Both experimental and analytical results show that the error floor experienced with nonpilot-aided transmission methods is effectively removed by the TCT scheme, resulting in significant performance gains at high signal-to-noise ratio values. The paper also examines the TCT system performance under typical operating conditions and presents a new analysis of the TCT theoretical error probability.

  19. Capacity of Cognitive Radio with Partial Channel Distribution Information in Rayleigh Fading Environments

    NASA Astrophysics Data System (ADS)

    Xu, D.; Li, Q.

    2015-11-01

    This paper investigates the capacity of the secondary user (SU) in a cognitive radio (CR) network in Rayleigh fading environments. Different from existing works where perfect channel state information (CSI) or channel distribution information (CDI) of the interference link from the SU to the primary user (PU) is assumed to be available, this paper assumes that only partial CDI is available. Specifically, we assume the distribution parameter is unknown and estimated from a set of channel gain samples. With such partial CDI, closed-form expressions for the ergodic and outage capacities of the SU are obtained under the transmit power and the interference outage constraints. It is shown that the capacity with partial CDI is not degraded compared to that with perfect CDI if the interference outage constraint is loose. It is also shown that the capacity can be significantly improved by increasing the number of channel gain samples.

  20. Estimation and Identification of Time-Varying Long-Term Fading Channels via the Particle Filter and the EM Algorithm

    SciTech Connect

    Ma, Xiao; Olama, Mohammed M; Djouadi, Seddik M; Charalambous, Prof. Charalambos

    2011-01-01

    In this paper, we are concerned with the estimation and identification of time-varying wireless long-term fading channels. The dynamics of the fading channels are captured using a mean-reverting linear stochastic differential equation driven by a Brownian motion. Recursive estimation and identification algorithms solely from received signal strength data are developed. These algorithms are based on combining the particle filter (PF) with the expectation maximization (EM) algorithm that estimate and identify the power path-loss of the channel and its parameters, respectively. Numerical results are provided to evaluate the accuracy of the proposed algorithms.

  1. Diversity technique for DAPSK signal over the frequency-selective fading channel

    NASA Astrophysics Data System (ADS)

    Lee, Jong Y.; Chung, Young M.; Lee, Sang U.

    2001-10-01

    In this paper, a maximal ratio combining (MRC) and weighted maximal ratio combining (WMRC) diversity receiver are proposed. The MRC receiver makes a decision at each branch based on the minimum distance criterion. The performance of the MRC receiver is analyzed on the frequency-selective Rayleigh and Rician fading channels, in terms of the union bound for bit error probability. In addition, the WMRC receiver, which assigns weighting factors to the decision variable at each branch, based on the optimum decision boundaries, is proposed. The performance of the WMRC is investigated through the computer simulation and compared with those of MRC and equal gain combining (EGC). From the results, it is found that the performances of the WMRC and MRC are better than those of EGC on both the frequency-selective Rayleigh and Rician fading channels and performance improvements over the EGC are noticeable when the number of diversity branches is large as long as the root mean square (rms) delay is smaller than or equal to 10% of the symbol period.

  2. Energy efficient video summarization and transmission over a slow fading wireless channel

    NASA Astrophysics Data System (ADS)

    Li, Zhu; Zhai, Fan; Katsaggelos, Aggelos K.; Pappas, Thrasyvoulos N.

    2005-03-01

    With the deployment of 2.5G/3G cellular network infrastructure and large number of camera equipped cell phones, the demand for video enabled applications are high. However, for an uplink wireless channel, both the bandwidth and battery energy capability are limited in a mobile phone for the video communication. These technical problems need to be effectively addressed before the practical and affordable video applications can be made available to consumers. In this paper we investigate the energy efficient video communication solution through joint video summarization and transmission adaptation over a slow fading channel. Coding and modulation schemes, as well as packet transmission strategy are optimized and adapted to the unique packet arrival and delay characteristics of the video summaries. Operational energy efficiency -- summary distortion performance is characterized under an optimal summarization setting.

  3. Time reversal communication in Rayleigh-fading broadcast channels with pinholes

    NASA Astrophysics Data System (ADS)

    Fannjiang, Albert C.

    2006-05-01

    The Letter presents an analysis of the time reversal in independent-multipath Rayleigh-fading channels with N inputs (transmitters) and M outputs (receivers). The main issues addressed are the condition of statistical stability, the rate of information transfer and the effect of pinholes. The stability condition is proved to be MC≪NB for broadband channels and M≪N for narrowband channels where C is the symbol rate, B is the bandwidth and N is the effective number (maybe less than 1) of transmitters. It is shown that when the number of screens, n-1, is relatively low compared to the logarithm of numbers of pinholes N is given by the harmonic (or inverse) sum of the number of transmitters and the numbers of pinholes at all screens. The novel idea of the effective number of time reversal array (TRA) elements is introduced to derive the stability condition and estimate the channel capacity in the presence of multi-screen pinholes. The information rate, under the constraints of the noise power ν per unit frequency and the average total power P, attains the supremum P/ν in the regime M∧N≫P/(νB). In particular, when N≫M≫P/(Bν) the optimal information rate can be achieved with statistically stable, sharply focused signals.

  4. Acoustic echo cancellation for full-duplex voice transmission on fading channels

    NASA Astrophysics Data System (ADS)

    Park, Sangil; Messer, Dion D.

    This paper discusses the implementation of an adaptive acoustic echo canceler for a hands-free cellular phone operating on a fading channel. The adaptive lattice structure, which is particularly known for faster convergence relative to the conventional tapped-delay-line (TDL) structure, is used in the initialization stage. After convergence, the lattice coefficients are converted into the coefficients for the TDL structure which can accommodate a larger number of taps in real-time operation due to its computational simplicity. The conversion method of the TDL coefficients from the lattice coefficients is derived and the DSP56001 assembly code for the lattice and TDL structure is included, as well as simulation results and the schematic diagram for the hardware implementation.

  5. Multilevel Concatenated Block Modulation Codes for the Frequency Non-selective Rayleigh Fading Channel

    NASA Technical Reports Server (NTRS)

    Lin, Shu; Rhee, Dojun

    1996-01-01

    This paper is concerned with construction of multilevel concatenated block modulation codes using a multi-level concatenation scheme for the frequency non-selective Rayleigh fading channel. In the construction of multilevel concatenated modulation code, block modulation codes are used as the inner codes. Various types of codes (block or convolutional, binary or nonbinary) are being considered as the outer codes. In particular, we focus on the special case for which Reed-Solomon (RS) codes are used as the outer codes. For this special case, a systematic algebraic technique for constructing q-level concatenated block modulation codes is proposed. Codes have been constructed for certain specific values of q and compared with the single-level concatenated block modulation codes using the same inner codes. A multilevel closest coset decoding scheme for these codes is proposed.

  6. An integrated diversity and fusion framework for binary consensus over fading channels

    NASA Astrophysics Data System (ADS)

    Malmirchegini, Mehrzad; Mostofi, Yasamin

    2013-12-01

    In this paper, we consider a cooperative network that is trying to reach consensus on the occurrence of an event by communicating over not fully connected and time-invariant network topologies with fading channels. We first discuss the fusion and diversity decision-making strategies over time-invariant network topologies and shed light on the underlying trade-offs. We then propose an integrated diversity and fusion framework. Our approach properly takes advantage of both fusion to enable information flow and diversity to increase robustness to link errors. We mathematically analyze the proposed framework and show how the network achieves accurate consensus asymptotically. To show an example, we then utilize the proposed framework over regular ring lattice networks. Our theoretical and simulation results indicate that the proposed technique improves the consensus performance considerably.

  7. SER performance analysis of MPPM FSO system with three decision thresholds over exponentiated Weibull fading channels

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Yang, Bensheng; Guo, Lixin; Shang, Tao

    2015-11-01

    In this work, the symbol error rate (SER) performance of the multiple pulse position modulation (MPPM) based free-space optical communication (FSO) system with three different decision thresholds, fixed decision threshold (FDT), optimized decision threshold (ODT) and dynamic decision threshold (DDT) over exponentiated Weibull (EW) fading channels has been investigated in detail. The effects of aperture averaging on each decision threshold under weak-to-strong turbulence conditions are further studied and compared. The closed-form SER expressions for three thresholds derived with the help of generalized Gauss-Laguerre quadrature rule are verified by the Monte Carlo simulations. This work is helpful for the design of receivers for FSO communication systems.

  8. A Power-Efficient Clustering Protocol for Coal Mine Face Monitoring with Wireless Sensor Networks Under Channel Fading Conditions.

    PubMed

    Ren, Peng; Qian, Jiansheng

    2016-01-01

    This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face. PMID:27338380

  9. A Power-Efficient Clustering Protocol for Coal Mine Face Monitoring with Wireless Sensor Networks Under Channel Fading Conditions

    PubMed Central

    Ren, Peng; Qian, Jiansheng

    2016-01-01

    This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face. PMID:27338380

  10. Analysis of fading in the propagation channel for the ORCA laser communication system

    NASA Astrophysics Data System (ADS)

    Sauer, Paul R.; Phillips, Ronald L.; Andrews, Larry C.; Wayne, David T.; Leclerc, Troy T.

    2011-06-01

    Irradiance data were collected over an air-to-ground path using several different sized receiving apertures. The data were collected from the Optical RF Communications Adjunct (ORCA) tracking beacon. The receiver system consisted of three telescopes of sizes 51 mm, 137 mm, and 272 mm. Probability of fade, number of fades per second, and mean fade time was computed for various intensity levels for irradiance data collected on all three telescopes. These measured statistics are compared to fading models derived from lognormal and gamma-gamma probability density function (PDF) models. Discussion is centered on the viability of these models under various conditions and on the presence of aero-optic effects. The gamma-gamma and lognormal model are found to be insufficient to model all fading statistics.

  11. On the capacity of MISO FSO systems over gamma-gamma and misalignment fading channels.

    PubMed

    Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Beatriz; Castillo-Vázquez, Carmen

    2015-08-24

    In this work, the ergodic capacity performance for multiple-input/single-output (MISO) free-space optical (FSO) communications system with equal gain combining (EGC) reception is analyzed over gamma-gamma and misalignment fading channels, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.). Novel and analytical closed-form ergodic capacity expression is obtained in terms of H-Fox function by using the well-known inequality between arithmetic and geometric mean of positive random variables (RV) in order to obtain an approximate closed-form expression of the distribution of the sum of M gamma-gamma with pointing errors variates. In addition, we present an asymptotic ergodic capacity expression at high signal-to-noise ratio (SNR) for the ergodic capacity of MISO FSO systems. It can be concluded that the use of MISO technique can significantly reduce the effect of the atmospheric turbulence as well as pointing errors and, hence, provide significant capacity gain over the direct path link (DL). The impact of pointing errors on the MISO FSO system is also analyzed, which only depends on the number of laser sources and pointing error parameters. Moreover, it can be also concluded that the ergodic capacity performance is dramatically reduced as a consequence of the severity of pointing error effects. Simulation results are further demonstrated to confirm the analytical results.

  12. Outage performance of MIMO FSO links over strong turbulence and misalignment fading channels.

    PubMed

    García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2011-07-01

    Atmospheric turbulence produces fluctuations in the irradiance of the transmitted optical beam, which is known as atmospheric scintillation, severely degrading the performance over free-space optical (FSO) links. Additionally, since FSO systems are usually installed on high buildings, building sway causes vibrations in the transmitted beam, leading to an unsuitable alignment between transmitter and receiver and, hence, a greater deterioration in performance. In this paper, the outage probability as a performance measure for multiple-input/multiple-output (MIMO) FSO communication systems with intensity modulation and direct detection (IM/DD) over strong atmospheric turbulence channels with pointing errors is analyzed. Novel closed-form expressions for the outage probability as well as their corresponding asymptotic expressions are presented when the irradiance of the transmitted optical beam is susceptible to either strong turbulence conditions, following a negative exponential distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results show that the diversity order is independent of the pointing error when the equivalent beam radius at the receiver is at least twice the value of the pointing error displacement standard deviation at the receiver. Simulation results are further demonstrated to confirm the analytical results. Additionally, since proper FSO transmission requires transmitters with accurate control of their beamwidth, asymptotic expressions here obtained for different diversity techniques are used to find the optimum beamwidth that minimizes the outage performance.

  13. Multidimensional Trellis Coded Phase Modulation Using a Multilevel Concatenation Approach. Part 2; Codes for AWGN and Fading Channels

    NASA Technical Reports Server (NTRS)

    Rajpal, Sandeep; Rhee, DoJun; Lin, Shu

    1997-01-01

    In this paper, we will use the construction technique proposed in to construct multidimensional trellis coded modulation (TCM) codes for both the additive white Gaussian noise (AWGN) and the fading channels. Analytical performance bounds and simulation results show that these codes perform very well and achieve significant coding gains over uncoded reference modulation systems. In addition, the proposed technique can be used to construct codes which have a performance/decoding complexity advantage over the codes listed in literature.

  14. Diversity detection in non-Gaussian noise employing the generalized approach to signal processing in noise with fading diversity channels

    NASA Astrophysics Data System (ADS)

    Tuzlukov, Vyacheslav

    2011-06-01

    In this paper, we consider the problem of M-ary signal detection based on the generalized approach to signal processing (GASP) in noise over a single-input multiple-output (SIMO) channel affected by frequency-dispersive Rayleigh distributed fading and corrupted by additive non-Gaussian noise modeled as spherically invariant random process. We derive both the optimum generalized detector (GD) structure based on GASP and a suboptimal reduced-complexity GD applying the low energy coherence approach jointly with the GASP in noise. Both GD structures are independent of the actual noise statistics. We also carry out a performance analysis of both GDs and compare with the conventional receivers. The performance analysis is carried out with reference to the case that the channel is affected by a frequency-selective fading and for a binary frequency-shift keying (BFSK) signaling format. The results obtained through both a Chernoff-bounding technique and Monte Carlo simulations reveal that the adoption of diversity also represents a suitable means to restore performance in the presence of dispersive fading and impulsive non-Gaussian noise. It is also shown that the suboptimal GD incurs a limited loss with respect to the optimum GD and this loss is less in comparison with the conventional receiver.

  15. Forward error correction and spatial diversity techniques for high-data-rate MILSATCOM over a slow-fading, nuclear-disturbed channel

    NASA Astrophysics Data System (ADS)

    Paul, Heywood I.; Meader, Charles B.; Lyons, Daniel A.; Ayers, David R.

    Forward error correction (FEC) and spatial diversity techniques are considered for improving the reliability of high-data-rate military satellite communication (MILSATCOM) over a slow-fading, nuclear-disturbed channel. Slow fading, which occurs when the channel decorrelation time is much greater than the transmitted symbol interval, is characterized by deep fades and, without special precautions, long bursts of errors over high-data-rate communication links. Using the widely accepted Defense Nuclear Agency (DNA) nuclear-scintillated channel model, the authors derive performance tradeoffs among required interleaver storage, FEC, spatial diversity, and link signal-to-noise ratio for differential binary phase shift keying (DBPSK) in the slow-fading environment. Spatial diversity is found to yield impressive gains without the large memory storage and transmission relay requirements associated with interleaving.

  16. Outage Capacity of Spectrum Sharing Cognitive Radio with Channel Estimation Errors and Feedback Delay in Rayleigh Fading Environments

    NASA Astrophysics Data System (ADS)

    Xu, D.; Feng, Z.; Zhang, P.

    2013-04-01

    This paper considers a spectrum sharing cognitive radio (CR) network consisting of one secondary user (SU) and one primary user (PU) in Rayleigh fading environments. The channel state information (CSI) between the secondary transmitter (STx) and the primary receiver (PRx) is assumed to be imperfect. Particularly, this CSI is assumed to be not only having channel estimation errors but also outdated due to feedback delay, which is different from existing work. We derive the closed-form expression for the outage capacity of the SU with this imperfect CSI under the average interference power constraint at the PU. Analytical results confirmed by simulations are presented to show the effect of the imperfect CSI. Particularly, it is shown that the outage capacity of the SU is robust to the channel estimation errors and feedback delay for low outage probability and high channel estimation errors and feedback delay.

  17. Effects of non-uniform windowing in a Rician-fading channel and simulation of adaptive automatic repeat request protocols

    NASA Astrophysics Data System (ADS)

    Kmiecik, Chris G.

    1990-06-01

    Two aspects of digital communication were investigated. In the first part, a Fast Fourier Transformation (FFT) based, M-ary frequency shift keying (FSK) receiver in a Rician-fading channel was analyzed to determine the benefits of non-uniform windowing of sampled received data. When a frequency offset occurs, non-uniform windowing provided better FFT magnitude separation. The improved dynamic range was balanced against a loss in detectability due to signal attenuation. With large frequency offset, the improved magnitude separation outweighed the loss in detectability. An analysis was carried out to determine what frequency deviation is necessary for non-uniform windowing to out-perform uniform windowing in a slow Rician-fading channel. Having established typical values of probability of bit errors, the second part of this thesis looked at improving throughput in a digital communications network by applying adaptive automatic repeat request (ARQ) protocols. The results of simulations of adaptive ARQ protocols with variable frame lengths is presented. By varying the frame length, improved throughput performance through all bit error rates was achieved.

  18. Performance of single and dual-polarized optically preamplified M-ary PPM systems with finite extinction ratios over FSO fading channels

    NASA Astrophysics Data System (ADS)

    Landolsi, Taha; Elrefaie, Aly F.

    2016-05-01

    M-ary pulse position modulation (PPM) systems have been considered in free-space optical (FSO) communications, optical fiber links, and passive optical networks. In this paper, we study the error performance of direct-detection optically preamplified M-ary PPM systems over slowly fading FSO channels. The study considers the combined effects on the probability of bit error, Pb, of channel fading with a given scintillation index, σp2, the transmitter finite extinction ratio, r, and the preamplifier spontaneous emission (ASE) noise. We provide results for both single and dual-polarized systems with symbol sizes M ∈ { 2, 4, …, 1024 } at Pb =10-4 and Pb =10-9. The fading models considered in this study are the exponential, log-normal, and gamma-gamma channels. For single-polarized systems with infinite extinction ratios, we provide closed-form expressions for the bit error probabilities for the three channel models. For the dual-polarized systems we compute them numerically. The results indicate that gamma-gamma fading imposes a more severe penalty than the log-normal case. In this study, the power penalty at Pb =10-9 ranges between 1.8 and 14 dB for the log-normal channel, whereas it ranges between 2.2 and 30.7 dB for the gamma-gamma channel. The study also demonstrates that the power penalty due to the combined effects of transmitter finite r and channel fading is the sum of the penalty due to fading alone and the penalty due to a finite r alone, and that the power penalty for dual-polarized systems is about 0.4 dB larger than single-polarized ones.

  19. SER Performance of Enhanced Spatial Multiplexing Codes with ZF/MRC Receiver in Time-Varying Rayleigh Fading Channels

    PubMed Central

    Lee, In-Ho

    2014-01-01

    We propose enhanced spatial multiplexing codes (E-SMCs) to enable various encoding rates. The symbol error rate (SER) performance of the E-SMC is investigated when zero-forcing (ZF) and maximal-ratio combining (MRC) techniques are used at a receiver. The proposed E-SMC allows a transmitted symbol to be repeated over time to achieve further diversity gain at the cost of the encoding rate. With the spatial correlation between transmit antennas, SER equations for M-ary QAM and PSK constellations are derived by using a moment generating function (MGF) approximation of a signal-to-noise ratio (SNR), based on the assumption of independent zero-forced SNRs. Analytic and simulated results are compared for time-varying and spatially correlated Rayleigh fading channels that are modelled as first-order Markovian channels. Furthermore, we can find an optimal block length for the E-SMC that meets a required SER. PMID:25114969

  20. Adaptive selective relaying in cooperative free-space optical systems over atmospheric turbulence and misalignment fading channels.

    PubMed

    Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2014-06-30

    In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results. PMID:24977911

  1. Adaptive selective relaying in cooperative free-space optical systems over atmospheric turbulence and misalignment fading channels.

    PubMed

    Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2014-06-30

    In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.

  2. Performance of the IEEE 802.11a Wireless Lan Standard Over Frequency-Selective, Slow, Ricean Fading Channels

    NASA Astrophysics Data System (ADS)

    Kao, Chi-han

    2002-09-01

    With the rapidly growing demand for more reliable and higher data rate wireless communications, the Institute of the Electrical and Electronics Engineers (IEEE) 802.11 working group approved a standard for 5-GHz band, Wireless Local Area Networks (WLAN) in 1999. This standard, IEEE 802.lla, supports data rates from 6 up to 54 Mbps and uses Orthogonal Frequency Division Multiplexing (OFDM) for transmission in indoor wireless environments. This thesis examines the performance of the IEEE 802.lla standard for different combinations of sub-carrier modulation type and code rate and determines the signal-to-noise ratio required to obtain a probability of bit error P(b) of 10-5. The channel is modeled as frequency-selective, slow, Ricean fading channel with Additive White Gaussian Noise (AWGN). Contrary to expectations, for the combinations of sub-carrier modulation type and code rate utilized by the IEEE 802.11a standard, some of the higher data rate combinations outperform some of the lower data rate combinations. On the other hand, the results also show significant coding gain when applying convolutional coding with Viterbi decoding, and hence highlight the importance of Forward Error Correction (FEC) coding to the performance of wireless communications systems.

  3. Beamforming effects on generalized Nakagami imaging.

    PubMed

    Yu, Xue; Guo, Yuexin; Huang, Sheng-Min; Li, Meng-Lin; Lee, Wei-Ning

    2015-10-01

    Ultrasound tissue characterization is crucial for the detection of tissue abnormalities. Since the statistics of the backscattered ultrasound signals strongly depend on density and spatial arrangement of local scatterers, appropriate modeling of the backscattered signals may be capable of providing unique physiological information on local tissue properties. Among various techniques, the Nakagami imaging, realized in a window-based estimation scheme, has a good performance in assessing different scatterer statistics in tissues. However, inconsistent m values have been reported in literature and obtained only from a local tissue region, abating the reliability of Nakagami imaging in tissue characterization. The discrepancies in m values in relevant literature may stem from the nonuniformity of the ultrasound image resolution, which is often neglected. We therefore hypothesized that window-based Nakagami m estimation was highly associated with the regional spatial resolution of ultrasound imaging. To test this hypothesis, our study investigated the effect of beamforming methods, including synthetic aperture (SA), coherent plane wave compounding (CPWC), multi-focusing (MF), and single-focusing (SF), on window-based m parameter estimation from the perspective of the resolution cell. The statistics of m parameter distribution as a function of imaging depth were characterized by their mean, variance, and skewness. The phantom with a low scatterer density (16 scatterers mm(-3)) had significantly lower m values compared to the ones with high scatterer densities (32 and 64 scatterers mm(-3)). Results from the homogeneous phantom with 64 scatterers mm(-3) showed that SA, MF, and CPWC had relatively uniform lateral resolutions compared to SF and thus relatively constant m estimates at different imaging depths. Our findings suggest that an ultrasound imaging regime exhibiting invariant spatial resolution throughout the entire imaging field of view would be the most appropriate

  4. Outage Performance Analysis of Relay Selection Schemes in Wireless Energy Harvesting Cooperative Networks over Non-Identical Rayleigh Fading Channels.

    PubMed

    Do, Nhu Tri; Bao, Vo Nguyen Quoc; An, Beongku

    2016-02-26

    In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source's radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks.

  5. Entanglement generation via non-Gaussian transfer over atmospheric fading channels

    NASA Astrophysics Data System (ADS)

    Hosseinidehaj, Nedasadat; Malaney, Robert

    2015-12-01

    In this work we probe the usefulness of non-Gaussian entangled states as a resource for quantum communication through atmospheric channels. We outline the initial conditions in which non-Gaussian state transfer leads to enhanced entanglement transfer relative to that obtainable via Gaussian state transfer. However, we conclude that in (anticipated) operational scenarios—where most of the non-Gaussian states to be transferred over the air are created just in time via photonic subtraction, addition, or replacement from incoming Gaussian states—the entanglement-generation rate between stations via non-Gaussian state transfer will be substantially less than that created by direct Gaussian state transfer. The role of postselection, distillation, and quantum memory in altering this conclusion is discussed, and comparison with entanglement rates produced via single-photon technologies is provided. Our results suggest that in the near term entangled Gaussian states, squeezed beyond some modest level, offer the most attractive proposition for the distribution of entanglement through high-loss atmospheric channels. The implications of our results for entanglement-based quantum key distribution to low-Earth orbit are presented.

  6. Improved BDF relaying scheme using time diversity over atmospheric turbulence and misalignment fading channels.

    PubMed

    García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2014-01-01

    A novel bit-detect-and-forward (BDF) relaying scheme based on repetition coding with the relay is proposed, significantly improving the robustness to impairments proper to free-space optical (FSO) communications such as unsuitable alignment between transmitter and receiver as well as fluctuations in the irradiance of the transmitted optical beam due to the atmospheric turbulence. Closed-form asymptotic bit-error-rate (BER) expressions are derived for a 3-way FSO communication setup. Fully exploiting the potential time-diversity available in the relay turbulent channel, a relevant better performance is achieved, showing a greater robustness to the relay location since a high diversity gain is provided regardless of the source-destination link distance.

  7. Improved BDF Relaying Scheme Using Time Diversity over Atmospheric Turbulence and Misalignment Fading Channels

    PubMed Central

    García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2014-01-01

    A novel bit-detect-and-forward (BDF) relaying scheme based on repetition coding with the relay is proposed, significantly improving the robustness to impairments proper to free-space optical (FSO) communications such as unsuitable alignment between transmitter and receiver as well as fluctuations in the irradiance of the transmitted optical beam due to the atmospheric turbulence. Closed-form asymptotic bit-error-rate (BER) expressions are derived for a 3-way FSO communication setup. Fully exploiting the potential time-diversity available in the relay turbulent channel, a relevant better performance is achieved, showing a greater robustness to the relay location since a high diversity gain is provided regardless of the source-destination link distance. PMID:24587711

  8. Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels

    DOE PAGES

    Olama, Mohammed M.; Djouadi, Seddik M.; Li, Yanyan; Fathy, Aly

    2013-01-01

    Stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean-square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and nonresolvable multipath received signals are considered and represented as small-scaled Nakagami fading. Themore » proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method’s viability and the results are presented.« less

  9. Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels

    SciTech Connect

    Olama, Mohammed M; Djouadi, Seddik M; Li, Yanyan; Fathy, Aly

    2013-01-01

    In this paper, stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and non-resolvable multipath received signals are considered and represented as small-scaled Nakagami fading. The proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method s viability and the results are presented.

  10. Performance evaluation of receive-diversity free-space optical communications over correlated Gamma-Gamma fading channels.

    PubMed

    Yang, Guowei; Khalighi, Mohammad-Ali; Ghassemlooy, Zabih; Bourennane, Salah

    2013-08-20

    The efficacy of spatial diversity in practical free-space optical communication systems is impaired by the fading correlation among the underlying subchannels. We consider in this paper the generation of correlated Gamma-Gamma random variables in view of evaluating the system outage probability and bit-error-rate under the condition of correlated fading. Considering the case of receive-diversity systems with intensity modulation and direct detection, we propose a set of criteria for setting the correlation coefficients on the small- and large-scale fading components based on scintillation theory. We verify these criteria using wave-optics simulations and further show through Monte Carlo simulations that we can effectively neglect the correlation corresponding to the small-scale turbulence in most practical systems, irrespective of the specific turbulence conditions. This has not been clarified before, to the best of our knowledge. We then present some numerical results to illustrate the effect of fading correlation on the system performance. Our conclusions can be generalized to the cases of multiple-beam and multiple-beam multiple-aperture systems.

  11. Fading In

    ERIC Educational Resources Information Center

    Nader, Karim; Wang, Szu-Han

    2006-01-01

    Patient H.M. can form new memories and maintain them for a few seconds before they fade away. From a neurobiological perspective, this amnesia is usually attributed to the absence of memory consolidation, that is, memory storage. An alternative view holds that this impairment reflects that the memory is present but cannot be retrieved. This debate…

  12. Fading Skies

    ERIC Educational Resources Information Center

    Sio, Betsy Menson

    2009-01-01

    A sky fading from blue to white to red at the horizon, and water darkening from light to midnight blue. Strong diagonals slashing through the image, drawing a viewer's eyes deeper into the picture, and delicate trees poised to convey a sense of beauty. These are the fascinating strengths of the ukiyo-e woodblock prints of Japanese artist Ando…

  13. Multimedia Transmission Over Cognitive Radio Channels Under Sensing Uncertainty

    NASA Astrophysics Data System (ADS)

    Ye, Chuang; Ozcan, Gozde; Gursoy, M. Cenk; Velipasalar, Senem

    2016-02-01

    This paper studies the performance of hierarchical modulation-based multimedia transmission in cognitive radio (CR) systems with imperfect channel sensing results under constraints on both transmit and interference power levels. Unequal error protection (UEP) of data transmission using hierarchical quadrature amplitude modulation (HQAM) is considered in which high priority (HP) data is protected more than low priority (LP) data. In this setting, closed-form bit error rate (BER) expressions for HP data and LP data are derived in Nakagami-$m$ fading channels in the presence of sensing errors. Subsequently, the optimal power control that minimizes weighted sum of average BERs of HP bits and LP bits or its upper bound subject to peak/average transmit power and average interference power constraints is derived and a low-complexity power control algorithm is proposed. Power levels are determined in three different scenarios, depending on the availability of perfect channel side information (CSI) of the transmission and interference links, statistical CSI of both links, or perfect CSI of the transmission link and imperfect CSI of the interference link. The impact of imperfect channel sensing decisions on the error rate performance of cognitive transmissions is also evaluated. In addition, tradeoffs between the number of retransmissions, the severity of fading, and peak signal-to-noise ratio (PSNR) quality are analyzed numerically. Moreover, performance comparisons of multimedia transmission with conventional quadrature amplitude modulation (QAM) and HQAM, and the proposed power control strategies are carried out in terms of the received data quality and number of retransmissions.

  14. Fade-Free Mobile Communication

    NASA Technical Reports Server (NTRS)

    Stevenson, C. R.

    1986-01-01

    Scheme for mobile communication reduces multipath fading and interference between adjacent channels. Proposed communication system lends itself to almost completely digital implementation, eliminating costly and bulky crystal filters. Scheme suitable for satellite-aided or terrestrial mobile communication, including cellular mobile telephony, at frequencies in 150-to-900-MHz range.

  15. Acoustic structure quantification by using ultrasound Nakagami imaging for assessing liver fibrosis.

    PubMed

    Tsui, Po-Hsiang; Ho, Ming-Chih; Tai, Dar-In; Lin, Ying-Hsiu; Wang, Chiao-Yin; Ma, Hsiang-Yang

    2016-01-01

    Acoustic structure quantification (ASQ) is a recently developed technique widely used for detecting liver fibrosis. Ultrasound Nakagami parametric imaging based on the Nakagami distribution has been widely used to model echo amplitude distribution for tissue characterization. We explored the feasibility of using ultrasound Nakagami imaging as a model-based ASQ technique for assessing liver fibrosis. Standard ultrasound examinations were performed on 19 healthy volunteers and 91 patients with chronic hepatitis B and C (n = 110). Liver biopsy and ultrasound Nakagami imaging analysis were conducted to compare the METAVIR score and Nakagami parameter. The diagnostic value of ultrasound Nakagami imaging was evaluated using receiver operating characteristic (ROC) curves. The Nakagami parameter obtained through ultrasound Nakagami imaging decreased with an increase in the METAVIR score (p < 0.0001), representing an increase in the extent of pre-Rayleigh statistics for echo amplitude distribution. The area under the ROC curve (AUROC) was 0.88 for the diagnosis of any degree of fibrosis (≥F1), whereas it was 0.84, 0.69, and 0.67 for ≥F2, ≥F3, and ≥F4, respectively. Ultrasound Nakagami imaging is a model-based ASQ technique that can be beneficial for the clinical diagnosis of early liver fibrosis. PMID:27605260

  16. Acoustic structure quantification by using ultrasound Nakagami imaging for assessing liver fibrosis

    PubMed Central

    Tsui, Po-Hsiang; Ho, Ming-Chih; Tai, Dar-In; Lin, Ying-Hsiu; Wang, Chiao-Yin; Ma, Hsiang-Yang

    2016-01-01

    Acoustic structure quantification (ASQ) is a recently developed technique widely used for detecting liver fibrosis. Ultrasound Nakagami parametric imaging based on the Nakagami distribution has been widely used to model echo amplitude distribution for tissue characterization. We explored the feasibility of using ultrasound Nakagami imaging as a model-based ASQ technique for assessing liver fibrosis. Standard ultrasound examinations were performed on 19 healthy volunteers and 91 patients with chronic hepatitis B and C (n = 110). Liver biopsy and ultrasound Nakagami imaging analysis were conducted to compare the METAVIR score and Nakagami parameter. The diagnostic value of ultrasound Nakagami imaging was evaluated using receiver operating characteristic (ROC) curves. The Nakagami parameter obtained through ultrasound Nakagami imaging decreased with an increase in the METAVIR score (p < 0.0001), representing an increase in the extent of pre-Rayleigh statistics for echo amplitude distribution. The area under the ROC curve (AUROC) was 0.88 for the diagnosis of any degree of fibrosis (≥F1), whereas it was 0.84, 0.69, and 0.67 for ≥F2, ≥F3, and ≥F4, respectively. Ultrasound Nakagami imaging is a model-based ASQ technique that can be beneficial for the clinical diagnosis of early liver fibrosis. PMID:27605260

  17. ACTS Rain Fade Compensation

    NASA Technical Reports Server (NTRS)

    Coney, Thom A.

    1996-01-01

    Performance status of the Adaptive Rain Fade Compensation includes: (1) The rain fade protocol is functional detecting fades, providing an additional 10 dB of margin and seamless transitions to and from coded operation; (2) The stabilization of the link margins and the optimization of rain fade decision thresholds has resulted in improved BER performance; (3) Characterization of the fade compensation algorithm is ongoing.

  18. Impact of nonzero boresight pointing errors on the performance of a relay-assisted free-space optical communication system over exponentiated Weibull fading channels.

    PubMed

    Wang, Ping; Liu, Xiaoxia; Cao, Tian; Fu, Huihua; Wang, Ranran; Guo, Lixin

    2016-09-20

    The impact of nonzero boresight pointing errors on the system performance of decode-and-forward protocol-based multihop parallel optical wireless communication systems is studied. For the aggregated fading channel, the atmospheric turbulence is simulated by an exponentiated Weibull model, and pointing errors are described by one recently proposed statistical model including both boresight and jitter. The binary phase-shift keying subcarrier intensity modulation-based analytical average bit error rate (ABER) and outage probability expressions are achieved for a nonidentically and independently distributed system. The ABER and outage probability are then analyzed with different turbulence strengths, receiving aperture sizes, structure parameters (P and Q), jitter variances, and boresight displacements. The results show that aperture averaging offers almost the same system performance improvement with boresight included or not, despite the values of P and Q. The performance enhancement owing to the increase of cooperative path (P) is more evident with nonzero boresight than that with zero boresight (jitter only), whereas the performance deterioration because of the increasing hops (Q) with nonzero boresight is almost the same as that with zero boresight. Monte Carlo simulation is offered to verify the validity of ABER and outage probability expressions.

  19. Performance of Reverse-Link Synchronous DS-CDMA System on a Frequency-Selective Multipath Fading Channel with Imperfect Power Control

    NASA Astrophysics Data System (ADS)

    Hwang, Seung-Hoon; Kim, Duk Kyung

    2002-12-01

    We analyze the performance for reverse-link synchronous DS-CDMA system in a frequency-selective Rayleigh fading channel with an imperfect power control scheme. The performance degradation due to power control error (PCE), which is approximated by a log-normally distributed random variable, is estimated as a function of the standard deviation of the PCE. In addition, we investigate the impacts of the multipath intensity profile (MIP) shape and the number of resolvable paths on the performance. Finally, the coded bit error performance is evaluated in order to estimate the system capacity. Comparing with the conventional CDMA system, we show an achievable gain of from 59% to 23% for reverse-link synchronous transmission technique (RLSTT) in the presence of imperfect power control over asynchronous transmission for[InlineEquation not available: see fulltext.]. As well, the effect of tradeoff between orthogonality and diversity can be seen according to the number of multipaths, and the tendency is kept even in the presence of PCE. We conclude that the capacity can be further improved via the RLSTT, because the DS-CDMA system is very sensitive to power control imperfections.

  20. Indoor radio channel modeling and mitigation of fading effects using linear and circular polarized antennas in combination for smart home system at 868 MHz

    NASA Astrophysics Data System (ADS)

    Wunderlich, S.; Welpot, M.; Gaspard, I.

    2014-11-01

    The markets for smart home products and services are expected to grow over the next years, driven by the increasing demands of homeowners considering energy monitoring, management, environmental controls and security. Many of these new systems will be installed in existing homes and offices and therefore using radio based systems for cost reduction. A drawback of radio based systems in indoor environments are fading effects which lead to a high variance of the received signal strength and thereby to a difficult predictability of the encountered path loss of the various communication links. For that reason it is necessary to derive a statistical path loss model which can be used to plan a reliable and cost effective radio network. This paper presents the results of a measurement campaign, which was performed in six buildings to deduce realistic radio channel models for a high variety of indoor radio propagation scenarios in the short range devices (SRD) band at 868 MHz. Furthermore, a potential concept to reduce the variance of the received signal strength using a circular polarized (CP) patch antenna in combination with a linear polarized antenna in an one-to-one communication link is presented.

  1. Impact of nonzero boresight pointing errors on the performance of a relay-assisted free-space optical communication system over exponentiated Weibull fading channels.

    PubMed

    Wang, Ping; Liu, Xiaoxia; Cao, Tian; Fu, Huihua; Wang, Ranran; Guo, Lixin

    2016-09-20

    The impact of nonzero boresight pointing errors on the system performance of decode-and-forward protocol-based multihop parallel optical wireless communication systems is studied. For the aggregated fading channel, the atmospheric turbulence is simulated by an exponentiated Weibull model, and pointing errors are described by one recently proposed statistical model including both boresight and jitter. The binary phase-shift keying subcarrier intensity modulation-based analytical average bit error rate (ABER) and outage probability expressions are achieved for a nonidentically and independently distributed system. The ABER and outage probability are then analyzed with different turbulence strengths, receiving aperture sizes, structure parameters (P and Q), jitter variances, and boresight displacements. The results show that aperture averaging offers almost the same system performance improvement with boresight included or not, despite the values of P and Q. The performance enhancement owing to the increase of cooperative path (P) is more evident with nonzero boresight than that with zero boresight (jitter only), whereas the performance deterioration because of the increasing hops (Q) with nonzero boresight is almost the same as that with zero boresight. Monte Carlo simulation is offered to verify the validity of ABER and outage probability expressions. PMID:27661587

  2. Outage Performance Analysis of Relay Selection Schemes in Wireless Energy Harvesting Cooperative Networks over Non-Identical Rayleigh Fading Channels

    PubMed Central

    Do, Nhu Tri; Bao, Vo Nguyen Quoc; An, Beongku

    2016-01-01

    In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source’s radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks. PMID:26927119

  3. Error performance analysis of FSO links with equal gain diversity receivers over double generalized gamma fading channels

    NASA Astrophysics Data System (ADS)

    Aminikashani, Mohammadreza; Kavehrad, Mohsen; Gu, Wenjun

    2016-02-01

    Free space optical (FSO) communication has been receiving increasing attention in recent years with its ability to achieve ultra-high data rates over unlicensed optical spectrum. A major performance limiting factor in FSO systems is atmospheric turbulence which severely degrades the system performance. To address this issue, multiple transmit and/or receive apertures can be employed, and the performance can be improved via diversity gain. In this paper, we investigate the bit error rate (BER) performance of FSO systems with transmit diversity or receive diversity with equal gain combining (EGC) over atmospheric turbulence channels described by the Double Generalized Gamma (Double GG) distribution. The Double GG distribution, recently proposed, generalizes many existing turbulence models in a closed-form expression and covers all turbulence conditions. Since the distribution function of a sum of Double GG random variables (RVs) appears in BER expression, we first derive a closed-form upper bound for the distribution of the sum of Double GG distributed RVs. A novel union upper bound for the average BER as well as corresponding asymptotic expression is then derived and evaluated in terms of Meijers G-functions.

  4. Modeling of errors in Nakagami imaging: illustration on breast mass characterization.

    PubMed

    Larrue, Aymeric; Noble, J Alison

    2014-05-01

    Nakagami imaging is an attractive tissue characterization method, as the parameter estimated at each location is related to properties of the tissues. The application to clinical ultrasound images is problematic, as the estimation of the parameters is disturbed by the presence of complex structures. We propose to consider separately the different aspects potentially affecting the value of the Nakagami parameters and quantify their effects on the estimation. This framework is applied to the classification of breast masses. Quantitative parameters are computed on two groups of ultrasound images of benign and malignant tumors. A statistical analysis of the result indicated that the previously observed difference between average values of the Nakagami parameters is explained mostly by estimation errors. In the future, new methods for reliable computation of Nakagami parameters need to be developed, and factors of error should be considered in studies using Nakagami parameters.

  5. Quantitative Ultrasonic Nakagami Imaging of Neck Fibrosis After Head and Neck Radiation Therapy

    SciTech Connect

    Yang, Xiaofeng; Yoshida, Emi; Cassidy, Richard J.; Beitler, Jonathan J.; Yu, David S.; Curran, Walter J.; Liu, Tian

    2015-06-01

    Purpose: To investigate the feasibility of ultrasound Nakagami imaging to quantitatively assess radiation-induced neck fibrosis, a common sequela of radiation therapy (RT) to the head and neck. Methods and Materials: In a pilot study, 40 study participants were enrolled and classified into 3 subgroups: (1) a control group of 12 healthy volunteers; (2) an asymptomatic group of 11 patients who had received intensity modulated RT for head and neck cancer and had experienced no neck fibrosis; and (3) a symptomatic group of 17 post-RT patients with neck fibrosis. Each study participant underwent 1 ultrasound study in which scans were performed in the longitudinal orientation of the bilateral neck. Three Nakagami parameters were calculated to quantify radiation-induced tissue injury: Nakagami probability distribution function, shape, and scaling parameters. Physician-based assessments of the neck fibrosis were performed according to the Radiation Therapy Oncology Group late morbidity scoring scheme, and patient-based fibrosis assessments were rated based on symptoms such as pain and stiffness. Results: Major discrepancies existed between physician-based and patient-based assessments of radiation-induced fibrosis. Significant differences in all Nakagami parameters were observed between the control group and 2 post-RT groups. Moreover, significant differences in Nakagami shape and scaling parameters were observed among asymptomatic and symptomatic groups. Compared with the control group, the average Nakagami shape parameter value increased by 32.1% (P<.001), and the average Nakagami scaling parameter increased by 55.7% (P<.001) for the asymptomatic group, whereas the Nakagami shape parameter increased by 74.1% (P<.001) and the Nakagami scaling parameter increased by 83.5% (P<.001) for the symptomatic group. Conclusions: Ultrasonic Nakagami imaging is a potential quantitative tool to characterize radiation-induced asymptomatic and symptomatic neck fibrosis.

  6. Adaptive rain fade compensation

    NASA Technical Reports Server (NTRS)

    Rautio, J. C.

    1980-01-01

    A large available margin must be provided for satellite communications systems operating near 20 GHz, which occasionally experience fades due to rain attenuation. It is proposed that this margin may be achieved in high-capacity FDMA satellites by dynamically providing a large margin to those links which are experiencing deep fades, while maintaining a small fade margin on all others. Single-beam SCPC operation and multiple-beam, satellite-switched FDMA systems are described, and the optimization of the dynamic FDMA links in a severely fading environment is investigated. A solution is derived which takes into account: (1) transponder intermodulation distortion, (2) cochannel and cross-polarization antenna interference, and (3) rain fade characteristics. The sample system configuration presented shows that such systems reach availability levels approaching 0.9999 at Ka-Band.

  7. Nakagami imaging for detecting thermal lesions induced by high-intensity focused ultrasound in tissue.

    PubMed

    Rangraz, Parisa; Behnam, Hamid; Tavakkoli, Jahan

    2014-01-01

    High-intensity focused ultrasound induces focalized tissue coagulation by increasing the tissue temperature in a tight focal region. Several methods have been proposed to monitor high-intensity focused ultrasound-induced thermal lesions. Currently, ultrasound imaging techniques that are clinically used for monitoring high-intensity focused ultrasound treatment are standard pulse-echo B-mode ultrasound imaging, ultrasound temperature estimation, and elastography-based methods. On the contrary, the efficacy of two-dimensional Nakagami parametric imaging based on the distribution of the ultrasound backscattered signals to quantify properties of soft tissue has recently been evaluated. In this study, ultrasound radio frequency echo signals from ex vivo tissue samples were acquired before and after high-intensity focused ultrasound exposures and then their Nakagami parameter and scaling parameter of Nakagami distribution were estimated. These parameters were used to detect high-intensity focused ultrasound-induced thermal lesions. Also, the effects of changing the acoustic power of the high-intensity focused ultrasound transducer on the Nakagami parameters were studied. The results obtained suggest that the Nakagami distribution's scaling and Nakagami parameters can effectively be used to detect high-intensity focused ultrasound-induced thermal lesions in tissue ex vivo. These parameters can also be used to understand the degree of change in tissue caused by high-intensity focused ultrasound exposures, which could be interpreted as a measure of degree of variability in scatterer concentration in various parts of the high-intensity focused ultrasound lesion. PMID:24264647

  8. 3D ultrasound Nakagami imaging for radiation-induced vaginal fibrosis

    NASA Astrophysics Data System (ADS)

    Yang, Xiaofeng; Rossi, Peter; Shelton, Joseph; Bruner, Debrorah; Tridandapani, Srini; Liu, Tian

    2014-03-01

    Radiation-induced vaginal fibrosis is a debilitating side-effect affecting up to 80% of women receiving radiotherapy for their gynecological (GYN) malignancies. Despite the significant incidence and severity, little research has been conducted to identify the pathophysiologic changes of vaginal toxicity. In a previous study, we have demonstrated that ultrasound Nakagami shape and PDF parameters can be used to quantify radiation-induced vaginal toxicity. These Nakagami parameters are derived from the statistics of ultrasound backscattered signals to capture the physical properties (e.g., arrangement and distribution) of the biological tissues. In this paper, we propose to expand this Nakagami imaging concept from 2D to 3D to fully characterize radiation-induced changes to the vaginal wall within the radiation treatment field. A pilot study with 5 post-radiotherapy GYN patients was conducted using a clinical ultrasound scanner (6 MHz) with a mechanical stepper. A serial of 2D ultrasound images, with radio-frequency (RF) signals, were acquired at 1 mm step size. The 2D Nakagami shape and PDF parameters were calculated from the RF signal envelope with a sliding window, and then 3D Nakagami parameter images were generated from the parallel 2D images. This imaging method may be useful as we try to monitor radiation-induced vaginal injury, and address vaginal toxicities and sexual dysfunction in women after radiotherapy for GYN malignancies.

  9. Performance analysis of relay-aided free-space optical communication system over gamma-gamma fading channels with pointing errors

    NASA Astrophysics Data System (ADS)

    Fu, Hui-hua; Wang, Ping; Wang, Ran-ran; Liu, Xiao-xia; Guo, Li-xin; Yang, Yin-tang

    2016-07-01

    The average bit error rate ( ABER) performance of a decode-and-forward (DF) based relay-assisted free-space optical (FSO) communication system over gamma-gamma distribution channels considering the pointing errors is studied. With the help of Meijer's G-function, the probability density function (PDF) and cumulative distribution function (CDF) of the aggregated channel model are derived on the basis of the best path selection scheme. The analytical ABER expression is achieved and the system performance is then investigated with the influence of pointing errors, turbulence strengths and structure parameters. Monte Carlo (MC) simulation is also provided to confirm the analytical ABER expression.

  10. Tempel Fades into Night

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Quick Time Movie for PIA02140 Tempel Fades into Night

    This movie is made up of images taken by Deep Impact's flyby spacecraft after it turned around to capture last shots of a receding comet Tempel 1. Earlier, the mission's probe had smashed into the surface of Tempel 1, kicking up the fan-shaped plume of dust seen here behind the comet. These pictures were taken by the flyby craft's high-resolution camera over a period beginning 50 minutes after impact, and ending about 12 hours after impact. Impact occurred at 10:52 p.m. Pacific time, July 3, 2005.

  11. Ultrasonic Nakagami-parameter characterization of parotid-gland injury following head-and-neck radiotherapy: A feasibility study of late toxicity

    SciTech Connect

    Yang, Xiaofeng; Wu, Ning; Wang, Yuefeng; Tridandapani, Srini; Beitler, Jonathan J.; Yu, David S.; Curran, Walter J.; Liu, Tian; Bruner, Deborah W.

    2014-02-15

    Purpose: The study aims to investigate whether Nakagami parameters—estimated from the statistical distribution of the backscattered ultrasound radio-frequency (RF) signals—could provide a means for quantitative characterization of parotid-gland injury resulting from head-and-neck radiotherapy. Methods: A preliminary clinical study was conducted with 12 postradiotherapy patients and 12 healthy volunteers. Each participant underwent one ultrasound study in which ultrasound scans were performed in the longitudinal, i.e., vertical orientation on the bilateral parotids. For the 12 patients, the mean radiation dose to the parotid glands was 37.7 ± 9.5 Gy, and the mean follow-up time was 16.3 ± 4.8 months. All enrolled patients experienced grade 1 or 2 late salivary-gland toxicity (RTOG/EORTC morbidity scale). The normal parotid glands served as the control group. The Nakagami-scaling and Nakagami-shape parameters were computed from the RF data to quantify radiation-induced parotid-gland changes. Results: Significant differences in Nakagami parameters were observed between the normal and postradiotherapy parotid glands. Compared with the control group, the Nakagami-scaling parameter of the postradiotherapy group decreased by 25.8% (p < 0.001), and the Nakagami-shape parameter decreased by 31.3% (p < 0.001). The area under the receiver operating characteristic curve was 0.85 for the Nakagami-scaling parameter and was 0.95 for the Nakagami-shape parameter, which further demonstrated the diagnostic efficiency of the Nakagami parameters. Conclusions: Nakagami parameters could be used to quantitatively measure parotid-gland injury following head-and-neck radiotherapy. Moreover, the clinical feasibility was demonstrated and this study provides meaningful preliminary data for future clinical investigation.

  12. Effects of Estimators on Ultrasound Nakagami Imaging in Visualizing the Change in the Backscattered Statistics from a Rayleigh Distribution to a Pre-Rayleigh Distribution.

    PubMed

    Tsui, Po-Hsiang; Wan, Yung-Liang; Tai, Dar-In; Shu, Yu-Chen

    2015-08-01

    Ultrasound Nakagami imaging has recently attracted interest as an imaging technique for analyzing envelope statistics. Because the presence of structures has a strong effect on estimation of the Nakagami parameter, previous studies have indicated that Nakagami imaging should be used specifically for characterization of soft tissues with fewer structures, such as liver tissues. Typically, changes in the properties of the liver parenchyma cause the backscattered statistics to transform from a Rayleigh distribution to a pre-Rayleigh distribution, and this transformation can be visualized using a Nakagami imaging technique. However, different estimators result in different estimated values; thus, the performance of a Nakagami image may depend on the type of estimator used. This study explored the effects of various estimators on ultrasound Nakagami imaging to describe the backscattered statistics as they change from a Rayleigh distribution to a pre-Rayleigh distribution. Simulations and clinical measurements involving patients with liver fibrosis (n = 85) yielded image data that were used to construct B-mode and conventional Nakagami images based on the moment estimator (denoted as mINV images) and maximum-likelihood estimator (denoted as mML images). In addition, novel window-modulated compounding Nakagami images based on the moment estimator (denoted as mWMC images) were also obtained. The means and standard deviations of the Nakagami parameters were examined as a function of the backscattered statistics. The experimental results indicate that the mINV, mML and mWMC images enabled quantitative visualization of the change in backscattered statistics from a Rayleigh distribution to a pre-Rayleigh distribution. Importantly, the mWMC image is superior to both mINV and mML images because it simultaneously realizes sensitive detection of the backscattered statistics and a reduction of estimation variance for image smoothness improvement. We therefore recommend using m

  13. Earth-space links and fade-duration statistics

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz

    1995-01-01

    In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.

  14. Earth-Space Links and Fade-Duration Statistics

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz

    1996-01-01

    In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.

  15. A review of fade detection techniques

    NASA Technical Reports Server (NTRS)

    Pergal, F. J.

    1990-01-01

    Several proposed propagation fade detection techniques are reviewed in light of general requirements presented for beacon fade characterization. The discussion includes an analysis of phase lock versus frequency lock beacon tracking loops and of excess noise injection type radiometers. The Advanced Communications Technology Satellite (ACTS) beacon fade detection schemes proposed by the Communications Satellite Corporation and the Jet Propulsion Laboratory are examined along with the fade detection technique used by Harris in the Advanced Communications Technology Satellite (ACTS) low burst rate (LBR) terminal.

  16. The dynamics of rain-induced fades

    NASA Technical Reports Server (NTRS)

    Sweeney, Dennis G.; Bostian, Charles W.

    1992-01-01

    The dynamics of rain-induced fades on satellite radio links is studied by evaluating the rate at which the first Fresnel zone volume fills with rain. A compact expression for the fade slope on a terrestrial path is derived which shows that once the rain rate is specified, fade slope is very sensitive to differences in rain velocity. Thus, there is no unique relationship between fade slope and rain rate.

  17. Effects of fade distribution on a mobile satellite downlink and uplink performance in a frequency reuse cellular configuration

    NASA Technical Reports Server (NTRS)

    Boutin, Karl; Lecours, Michel; Pelletier, Marcel; Delisle, Gilles Y.

    1990-01-01

    In a mobile satellite system with a frequency reuse cellular configuration, significant co-channel interference can be experienced due to the antenna sidelobe level. The signal will be subjected not only to its own fading, but also to the effect of the varying degree of fading on co-channel interferer, and this interference will behave differently in the up and in the down link. This paper presents a quantitative evaluation of the combined effects of fades and co-channel interference on a mobile satellite link.

  18. Perceptual Fading without Retinal Adaptation

    ERIC Educational Resources Information Center

    Hsieh, Po-Jang; Colas, Jaron T.

    2012-01-01

    A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here…

  19. System for Processing Coded OFDM Under Doppler and Fading

    NASA Technical Reports Server (NTRS)

    Tsou, Haiping; Darden, Scott; Lee, Dennis; Yan, Tsun-Yee

    2005-01-01

    An advanced communication system has been proposed for transmitting and receiving coded digital data conveyed as a form of quadrature amplitude modulation (QAM) on orthogonal frequency-division multiplexing (OFDM) signals in the presence of such adverse propagation-channel effects as large dynamic Doppler shifts and frequency-selective multipath fading. Such adverse channel effects are typical of data communications between mobile units or between mobile and stationary units (e.g., telemetric transmissions from aircraft to ground stations). The proposed system incorporates novel signal processing techniques intended to reduce the losses associated with adverse channel effects while maintaining compatibility with the high-speed physical layer specifications defined for wireless local area networks (LANs) as the standard 802.11a of the Institute of Electrical and Electronics Engineers (IEEE 802.11a). OFDM is a multi-carrier modulation technique that is widely used for wireless transmission of data in LANs and in metropolitan area networks (MANs). OFDM has been adopted in IEEE 802.11a and some other industry standards because it affords robust performance under frequency-selective fading. However, its intrinsic frequency-diversity feature is highly sensitive to synchronization errors; this sensitivity poses a challenge to preserve coherence between the component subcarriers of an OFDM system in order to avoid intercarrier interference in the presence of large dynamic Doppler shifts as well as frequency-selective fading. As a result, heretofore, the use of OFDM has been limited primarily to applications involving small or zero Doppler shifts. The proposed system includes a digital coherent OFDM communication system that would utilize enhanced 802.1la-compatible signal-processing algorithms to overcome effects of frequency-selective fading and large dynamic Doppler shifts. The overall transceiver design would implement a two-frequency-channel architecture (see figure

  20. Extending the impulse response in order to reduce errors due to impulse noise and signal fading

    NASA Technical Reports Server (NTRS)

    Webb, Joseph A.; Rolls, Andrew J.; Sirisena, H. R.

    1988-01-01

    A finite impulse response (FIR) digital smearing filter was designed to produce maximum intersymbol interference and maximum extension of the impulse response of the signal in a noiseless binary channel. A matched FIR desmearing filter at the receiver then reduced the intersymbol interference to zero. Signal fades were simulated by means of 100 percent signal blockage in the channel. Smearing and desmearing filters of length 256, 512, and 1024 were used for these simulations. Results indicate that impulse response extension by means of bit smearing appears to be a useful technique for correcting errors due to impulse noise or signal fading in a binary channel.

  1. Nakagami Markov random field as texture model for ultrasound RF envelope image.

    PubMed

    Bouhlel, N; Sevestre-Ghalila, S

    2009-06-01

    The aim of this paper is to propose a new Markov random field (MRF) model for the backscattered ultrasonic echo in order to get information about backscatter characteristics, such as the scatterer density, amplitude and spacing. The model combines the Nakagami distribution that describes the envelope of backscattered echo with spatial interaction using MRF. In this paper, the parameters of the model and the estimation parameter method are introduced. Computer simulation using ultrasound radio-frequency (RF) simulator and experiments on choroidal malignant melanoma have been undertaken to test the validity of the model. The relationship between the parameters of MRF model and the backscatter characteristics has been established. Furthermore, the ability of the model to distinguish between normal and abnormal tissue has been proved. All the results can show the success of the model.

  2. Fade Mitigation Techniques at Ka-Band

    NASA Technical Reports Server (NTRS)

    Dissanayake, Asoka (Editor)

    1996-01-01

    Rain fading is the dominant propagation impairment affecting Ka-band satellite links and rain fade mitigation is a key element in the design of Ka-band satellite networks. Some of the common fade mitigation techniques include: power control, diversity, adaptive coding, and resource sharing. The Advanced Communications Technology Satellite (ACTS) provides an excellent opportunity to develop and test Ka-band rain impairment amelioration techniques. Up-link power control and diversity are discussed in this paper.

  3. Antifade sonar employs acoustic field diversity to recover signals from multipath fading

    SciTech Connect

    Lubman, D.

    1996-04-01

    Co-located pressure and particle motion (PM) hydrophones together with four-channel diversity combiners may be used to recover signals from multipath fading. Multipath fading is important in both shallow and deep water propagation and can be an important source of signal loss. The acoustic field diversity concept arises from the notion of conservation of signal energy and the observation that in rooms at least, the total acoustic energy density is the sum of potential energy (scalar field-sound pressure) and kinetic energy (vector field-sound PM) portions. One pressure hydrophone determines acoustic potential energy density at a point. In principle, three PM sensors (displacement, velocity, or acceleration) directed along orthogonal axes describe the kinetic energy density at a point. For a single plane wave, the time-averaged potential and kinetic field energies are identical everywhere. In multipath interference, however, potential and kinetic field energies at a point are partitioned unequally, depending mainly on relative signal phases. Thus, when pressure signals are in deep fade, abundant kinetic field signal energy may be available at that location. Performance benefits require a degree of uncorrelated fading between channels. The expectation of nearly uncorrelated fading is motivated from room theory. Performance benefits for sonar limited by independent Rayleigh fading are suggested by analogy to antifade radio. Average SNR can be improved by several decibels, holding time on target is multiplied manifold, and the bit error rate for data communication is reduced substantially. {copyright} {ital 1996 American Institute of Physics.}

  4. Effects of multipath fading on low data-rate space communications.

    NASA Technical Reports Server (NTRS)

    Chen, C. H.

    1972-01-01

    Studies have shown that there is a severe signal fading at the turbulent atmosphere of a distant planet such as Venus. The data may be lost during deep fade. It is the objective of this paper to examine the effects of multipath fading on the performance of the noncoherent coded system which is used for the low data-rate space communications especially with the small probes. An exact error probability of the wideband noncoherent MFSK receiver is derived from using the 'Rician' channel model. While the error performance of the receiver is worse than that of the ideal MFSK receiver, as expected, it is interesting to note that the performance degradation due to the multipath fading diminishes as the product of bit duration and IF filter bandwidth becomes large.

  5. When Does Fading Enhance Perceptual Category Learning?

    ERIC Educational Resources Information Center

    Pashler, Harold; Mozer, Michael C.

    2013-01-01

    Training that uses exaggerated versions of a stimulus discrimination (fading) has sometimes been found to enhance category learning, mostly in studies involving animals and impaired populations. However, little is known about whether and when fading facilitates learning for typical individuals. This issue was explored in 7 experiments. In…

  6. Microsaccades counteract visual fading during fixation.

    PubMed

    Martinez-Conde, Susana; Macknik, Stephen L; Troncoso, Xoana G; Dyar, Thomas A

    2006-01-19

    Our eyes move continually, even while we fixate our gaze on an object. If fixational eye movements are counteracted, our perception of stationary objects fades completely, due to neural adaptation. Some studies have suggested that fixational microsaccades refresh retinal images, thereby preventing adaptation and fading. However, other studies disagree, and so the role of microsaccades remains unclear. Here, we correlate visibility during fixation to the occurrence of microsaccades. We asked subjects to indicate when Troxler fading of a peripheral target occurs, while simultaneously recording their eye movements with high precision. We found that before a fading period, the probability, rate, and magnitude of microsaccades decreased. Before transitions toward visibility, the probability, rate, and magnitude of microsaccades increased. These results reveal a direct link between suppression of microsaccades and fading and suggest a causal relationship between microsaccade production and target visibility during fixation.

  7. Cross-Sectional Nakagami Images in Passive Stretches Reveal Damage of Injured Muscles.

    PubMed

    Lin, Shih-Ping; Lin, Yi-Hsun; Fan, Shih-Chen; Huang, Bu-Miin; Lin, Wei-Yin; Wang, Shyh-Hau; Shung, K Kirk; Su, Fong-Chin; Wu, Chia-Ching

    2016-01-01

    Muscle strain is still awanting a noninvasive quantitatively diagnosis tool. High frequency ultrasound (HFU) improves image resolution for monitoring changes of tissue structures, but the biomechanical factors may influence ultrasonography during injury detection. We aim to illustrate the ultrasonic parameters to present the histological damage of overstretched muscle with the consideration of biomechanical factors. Gastrocnemius muscles from mice were assembled and ex vivo passive stretching was performed before or after injury. After injury, the muscle significantly decreased mechanical strength. Ultrasonic images were obtained by HFU at different deformations to scan in cross and longitudinal orientations of muscle. The ultrasonography was quantified by echogenicity and Nakagami parameters (NP) for structural evaluation and correlated with histological results. The injured muscle at its original length exhibited decreased echogenicity and NP from HFU images. Cross-sectional ultrasonography revealed a loss of correlation between NP and passive muscle stretching that suggested a special scatterer pattern in the cross section of injured muscle. The independence of NP during passive stretching of injured muscle was confirmed by histological findings in ruptured collagen fibers, decreased muscle density, and increased intermuscular fiber space. Thus, HFU analysis of NP in cross section represents muscle injury that may benefit the clinical diagnosis. PMID:27034946

  8. Cross-Sectional Nakagami Images in Passive Stretches Reveal Damage of Injured Muscles

    PubMed Central

    Lin, Shih-Ping; Lin, Yi-Hsun; Fan, Shih-Chen; Huang, Bu-Miin; Lin, Wei-Yin; Wang, Shyh-Hau; Shung, K. Kirk; Su, Fong-Chin; Wu, Chia-Ching

    2016-01-01

    Muscle strain is still awanting a noninvasive quantitatively diagnosis tool. High frequency ultrasound (HFU) improves image resolution for monitoring changes of tissue structures, but the biomechanical factors may influence ultrasonography during injury detection. We aim to illustrate the ultrasonic parameters to present the histological damage of overstretched muscle with the consideration of biomechanical factors. Gastrocnemius muscles from mice were assembled and ex vivo passive stretching was performed before or after injury. After injury, the muscle significantly decreased mechanical strength. Ultrasonic images were obtained by HFU at different deformations to scan in cross and longitudinal orientations of muscle. The ultrasonography was quantified by echogenicity and Nakagami parameters (NP) for structural evaluation and correlated with histological results. The injured muscle at its original length exhibited decreased echogenicity and NP from HFU images. Cross-sectional ultrasonography revealed a loss of correlation between NP and passive muscle stretching that suggested a special scatterer pattern in the cross section of injured muscle. The independence of NP during passive stretching of injured muscle was confirmed by histological findings in ruptured collagen fibers, decreased muscle density, and increased intermuscular fiber space. Thus, HFU analysis of NP in cross section represents muscle injury that may benefit the clinical diagnosis. PMID:27034946

  9. Fade-resistant forward error correction method for free-space optical communications systems

    DOEpatents

    Johnson, Gary W.; Dowla, Farid U.; Ruggiero, Anthony J.

    2007-10-02

    Free-space optical (FSO) laser communication systems offer exceptionally wide-bandwidth, secure connections between platforms that cannot other wise be connected via physical means such as optical fiber or cable. However, FSO links are subject to strong channel fading due to atmospheric turbulence and beam pointing errors, limiting practical performance and reliability. We have developed a fade-tolerant architecture based on forward error correcting codes (FECs) combined with delayed, redundant, sub-channels. This redundancy is made feasible though dense wavelength division multiplexing (WDM) and/or high-order M-ary modulation. Experiments and simulations show that error-free communications is feasible even when faced with fades that are tens of milliseconds long. We describe plans for practical implementation of a complete system operating at 2.5 Gbps.

  10. EM-Based Multiuser Detection in Fast Fading Multipath Environments

    NASA Astrophysics Data System (ADS)

    Borran, Mohammad Jaber; Aazhang, Behnaam

    2002-12-01

    We address the problem of multiuser detection in fast fading multipath environments for DS-CDMA systems. In fast fading scenarios, temporal variations of the channel cause significant performance degradation even with the Rake receiver. We use a previously introduced time-frequency (TF) Rake receiver based on a canonical formulation of the channel and signals to simultaneously combat fading and multipath effects. This receiver uses the Doppler spread caused by rapid time-varying channel as another means of diversity. In dealing with multiaccess interference and as an attempt to avoid the prohibitive computational complexity of the optimum maximum-likelihood (ML) detector, we use the expectation maximization (EM) algorithm to derive an approximate ML detector. The new detector turns out to have an iterative structure very similar to the well-known multistage detector with some extra parameters. At the two extreme values of these parameters, the EM detector reduces to either one-shot TF Rake or generalized multistage detector. For the intermediate values of the parameters, it combines the two estimates to obtain a better decision for the bits of the users. Because of using the EM algorithm, this detector has better convergence properties than the multistage detector; the bit estimates always converge, and if an appropriate initial vector is used, they converge to the global maximizer of the likelihood function. As a result, the new detector provides significantly improved performance while maintaining the low complexity of the multistage detector. Our simulation results confirm the expected performance improvements compared to the base case of the TF Rake as well as the multistage detector used with the TF Rake.

  11. Nicotinic antagonists produce differing amounts of tetanic fade in the isolated diaphragm of the rat.

    PubMed

    Gibb, A J; Marshall, I G

    1986-11-01

    The effects of nicotine antagonists on single twitches, trains of four twitches and tetanic contractions of the isolated diaphragm of the rat were examined. Different drugs were found to produce different amounts of tetanic fade relative to depression of twitch tension. The order of activity from most able, to least able to produce fade was: hexamethonium greater than trimetaphan=atracurium=tubocurarine greater than pancuronium greater than erabutoxin b. The effect of erabutoxin b was distinctive for its almost complete lack of tetanic fade. 3,4-Diaminopyridine increased tetanic fade produced by tubocurarine, atracurium and hexamethonium, but not that produced by erabutoxin b. It is concluded that nicotinic antagonists act at more than one site at the neuromuscular junction. Assuming block of the postjunctional acetylcholine receptor produces tension depression, a second or third site must be involved in producing tetanic fade. The possibility that tetanic fade results from block of the ion channel associated with the postjunctional acetylcholine receptor or from the block of a prejunctional nicotinic receptor is discussed.

  12. Differential reinforcement with and without instructional fading.

    PubMed

    Ringdahl, Joel E; Kitsukawa, Kana; Andelman, Marc S; Call, Nathan; Winborn, Lisa; Barretto, Anjali; Reed, Gregory K

    2002-01-01

    We evaluated a differential-reinforcement-based treatment package for the reduction of problem behavior during instructional situations. Differential reinforcement of alternative behavior (DRA; compliance) was implemented across two conditions. During one condition, instructions were presented approximately once every other minute. This condition was considered the terminal goal for treatment. During the second condition, the rate of instructions was gradually increased (beginning at zero and ending when instruction rate was similar to the first condition). Results indicated that DRA with instructional fading resulted in less problem behavior than DRA without instructional fading. These results are similar to previous studies regarding the utility of instructional fading.

  13. Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Context image for PIA03693 Channel

    This channel is located south of Iani Chaos.

    Image information: VIS instrument. Latitude -10.9N, Longitude 345.5E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  14. Simulating Rain Fade In A Communication System

    NASA Technical Reports Server (NTRS)

    Shalkhauser, Kurt A.; Nagy, Lawrence A.; Svoboda, James K.

    1994-01-01

    Automated, computer-controlled assembly of electronic equipment developed for use in simulation testing of downlink portion of Earth/satellite microwave digital communication system. Designed to show effects upon performance of system of rain-induced fading in received signal and increases in transmitted power meant to compensate for rain-induced fading. Design of communication system improved iteratively in response to results of simulations, leading eventually to design ensuring clear, uninterrupted transmission of digital signals.

  15. Fade-durations derived from land-mobile-satellite measurements in Australia

    NASA Technical Reports Server (NTRS)

    Hase, Yoshihiro; Vogel, Wolfhard J.; Goldhirsh, Julius

    1991-01-01

    Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.

  16. Fade-durations derived from land-mobile-satellite measurements in Australia

    NASA Astrophysics Data System (ADS)

    Hase, Yoshihiro; Vogel, Wolfhard J.; Goldhirsh, Julius

    1991-05-01

    Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.

  17. Visual and tactile assessment of neuromuscular fade.

    PubMed

    Brull, S J; Silverman, D G

    1993-08-01

    The accuracy of visual and tactile assessment of the neuromuscular fade in response to train-of-four (TOF) and double-burst stimulation (DBS) were compared to assess their relative utility in the clinical setting. For each of 74 data sets with a mechanographic TOF ratio less than 0.70, an observer (blinded to the presence or degree of fade) performed visual and tactile assessments of fade in response to TOF, DBS3,3, and DBS3,2 stimuli at low current (20 and 30 mA) and high current (50 and 60 mA). For the range of mechanographic TOF ratios between 0.41 and 0.70, visual assessment failed to identify TOF, DBS3,3, and DBS3,2 fade in 46%, 18%, and 14% of cases at high current and in 23%, 5%, and 0% of cases at low current, respectively. Tactile assessments failed to identify fade in 55%, 23%, and 14% of cases at high current and in 23%, 14%, and 14% of cases at low current. Overall, the ability to detect fade was comparable for visual and tactile assessments regardless of the method of neurostimulation (P = NS with paired t-test). However, the degree of overestimation of the fade ratio (i.e., quantitative assessment) tended to be less when using tactile means; the difference achieved significance for TOF at low current and DBS3,3 at both low and high currents. We conclude that the differences between the visual and tactile means of assessment are relatively small compared to the differences among the TOF and DBS patterns of neurostimulation. Both subjective techniques are often inadequate in settings in which assurance of full recovery of neuromuscular function is critical.

  18. Fade/non-fade duration characteristics of land mobile satellite communication link

    NASA Astrophysics Data System (ADS)

    Hase, Yoshihiro

    1992-07-01

    Fade and nonfade duration characteristics of land mobile satellite links, which have not been well studied previously, were analyzed. Data used for the analysis were obtained in South Eastern Australia by receiving L-band CW signals from the Engineering Test Satellite. Results of the analysis show that the cumulative distributions of fade and nonfade durations follow log-normal and power law patterns, respectively. Many other interesting results were also obtained, for example, that the distribution does not depend on a threshold level defining fade and nonfade durations. Phase fluctuations of received signals were also analyzed. They were generally small, allowing the link characteristics to be estimated from levels only.

  19. Experimental characterization and mitigation of turbulence induced signal fades within an ad hoc FSO network.

    PubMed

    Perez, Joaquin; Zvanovec, Stanislav; Ghassemlooy, Zabih; Popoola, Wasiu O

    2014-02-10

    Optical beams propagating through the turbulent atmospheric channel suffer from both the attenuation and phase distortion. Since future wireless networks are envisaged to be deployed in the ad hoc mesh topology, this paper presents the experimental laboratory characterization of mitigation of turbulence induced signal fades for two ad hoc scenarios. Results from measurements of the thermal structure constant along the propagation channels, changes of the coherence lengths for different turbulence regimes and the eye diagrams for partially correlated turbulences in free space optical channels are discussed. Based on these results future deployment of optical ad hoc networks can be more straightforwardly planned.

  20. Sources of Fading Effects of Prekindergarten Experience.

    ERIC Educational Resources Information Center

    Reynolds, Arthur J.

    This study investigated factors that play a role in the fading effects of prekindergarten programs for economically disadvantaged children. The school adjustment of 1,284 low-income, minority children in prekindergarten and kindergarten programs funded by the government (i.e., Child Parent Center; Head Start) was traced through the third year of…

  1. "Concreteness Fading" Promotes Transfer of Mathematical Knowledge

    ERIC Educational Resources Information Center

    McNeil, Nicole M.; Fyfe, Emily R.

    2012-01-01

    Recent studies have suggested that educators should avoid concrete instantiations when the goal is to promote transfer. However, concrete instantiations may benefit transfer in the long run, particularly if they are "faded" into more abstract instantiations. Undergraduates were randomly assigned to learn a mathematical concept in one of three…

  2. Optical scintillations and fade statistics for a satellite-communication system

    NASA Astrophysics Data System (ADS)

    Andrews, L. C.; Phillips, R. L.

    1995-11-01

    Estimates of the scintillation index, fractional fade time, expected number of fades, and mean duration of fade time associated with a propagating Gaussian-beam wave are developed for uplink and downlink laser satellite-communication channels. Estimates for the spot size of the beam at the satellite or the ground or airborne receiver are also provided. Weak-fluctuation theory based on the log-normal model is applicable for intensity fluctuations near the optical axis of the beam provided that the zenith angle is not too large, generally not exceeding 60 degrees. However, there is an increase in scintillations that occurs with increasing pointing error at any zenith angle, particularly for uplink channels. Large off-axis scintillations are of particular significance because they imply that small pointing errors can cause serious degradation in the communication-channel reliability. Off-axis scintillations increase more rapidly for larger-diameter beams and, in some cases, can lead to a radial saturation effect for pointing errors less than 1 =B5rad off the optical beam axis.

  3. Fade durations in satellite-path mobile radio propagation

    NASA Technical Reports Server (NTRS)

    Schmier, Robert G.; Bostian, Charles W.

    1986-01-01

    Fades on satellite to land mobile radio links are caused by several factors, the most important of which are multipath propagation and vegetative shadowing. Designers of vehicular satellite communications systems require information about the statistics of fade durations in order to overcome or compensate for the fades. Except for a few limiting cases, only the mean fade duration can be determined analytically, and all other statistics must be obtained experimentally or via simulation. This report describes and presents results from a computer program developed at Virginia Tech to simulate satellite path propagation of a mobile station in a rural area. It generates rapidly-fading and slowly-fading signals by separate processes that yield correct cumulative signal distributions and then combines these to simulate the overall signal. This is then analyzed to yield the statistics of fade duration.

  4. Observations of auroral fading before breakup

    NASA Technical Reports Server (NTRS)

    Pellinen, R. J.; Heikkila, W. J.

    1978-01-01

    The onset of auroral breakup was studied by using a variety of instruments with time resolution of some tens of second. Rapid sequences of all-sky photographs, and fast meridian scans by photometers, show that breakup is usually preceded by moderate brightening, followed by fading of the auroral brightness lasting one or two minutes, before the actual breakup itself. This optical activity is closely correlated with the development of auroral radar echoes. Data from a magnetometer network provide some indication of a correlated response by the local auroral and ionospheric currents. Riometer recordings show a slow decrease in ionspheric radio wave absorption over a period of about ten minutes prior to breakup, with the largest decrease essentially to quiet-time values in the region of auroral fading and subsequent breakup.

  5. Fading to increase heterosexual responsiveness in homosexuals1

    PubMed Central

    Barlow, David H.; Agras, W. Stewart

    1973-01-01

    Heterosexual responsiveness, measured by penile responses and reports of behavior, was strengthened in three homosexuals through a fading procedure. Using two slide projectors, colored slides of nude females were superimposed on colored slides of nude males. As the sexual response was emitted, the nude male was faded out and the nude female faded in. Heterosexual arousal decreased when the fading procedure was reversed or stopped and increased once again when fading was resumed. Homosexual arousal remained high during this experiment but had decreased in two subjects at follow-up. The results suggest that fading was responsible for altering stimulus control of sexual arousal and that aversive techniques may not be necessary in the treatment of sexual deviation. ImagesFig. 1 PMID:16795417

  6. Capacity fade in nickel cadmium and nickel hydrogen cells

    NASA Technical Reports Server (NTRS)

    Edgar, Tim; Hayden, Jeff; Pickett, David F.; Abrams-Blakemore, Bruce; Liptak, ED

    1993-01-01

    Research and operational experience with capacity fade in nickel cadmium and nickel hydrogen cells are summarized in outline form. The theoretical causes of capacity fade are reviewed and the role of cell storage, positive electrodes, and cobalt additives are addressed. Three examples of observed capacity fade are discussed: INTELSAT 5, INTELSAT 6, and an Explorer platform. Finally, prevention and recovery methods are addressed and the current status of Eagle Picher/Hughes research is discussed.

  7. Design of an anti-Rician-fading modem for mobile satellite communication systems

    NASA Technical Reports Server (NTRS)

    Kojima, Toshiharu; Ishizu, Fumio; Miyake, Makoto; Murakami, Keishi; Fujino, Tadashi

    1995-01-01

    To design a demodulator applicable to mobile satellite communication systems using differential phase shift keying modulation, we have developed key technologies including an anti-Rician-fading demodulation scheme, an initial acquisition scheme, automatic gain control (AGC), automatic frequency control (AFC), and bit timing recovery (BTR). Using these technologies, we have developed one-chip digital signal processor (DSP) modem for mobile terminal, which is compact, of light weight, and of low power consumption. Results of performance test show that the developed DSP modem achieves good performance in terms of bit error ratio in mobile satellite communication environment, i.e., Rician fading channel. It is also shown that the initial acquisition scheme acquires received signal rapidly even if the carrier-to-noise power ratio (CNR) of the received signal is considerably low.

  8. Overview of techniques for mitigation of fading and shadowing in the direct broadcast satellite radio environment

    NASA Technical Reports Server (NTRS)

    Bell, David; Gevargiz, John; Vaisnys, Arvydas; Julian, David

    1995-01-01

    The DBS radio propagation environment is divided into three sub-environments, indoor, rural-suburban mobile and urban mobile. Indoor propagation effects are in a large part determined by construction material. Non-metallic materials afford direct, albeit attenuated penetration of the satellite signal with a minimum of multipath signal scattering. Signal penetration into structures using significant metallic materials is often indirect, through openings such as doors and windows and propagation will involve significant multipath components. Even so, delay spread in many situations is on the order of 10's of nanoseconds resulting in relatively flat fading. Thus frequency diversity techniques such as Orthogonal Frequency Division Multiplex (OFDM) and Code Division Multiple Access (CDMA) or equalization techniques do not realize their intended performance enhancement. Antenna diversity, directivity and placement are key mitigation techniques for the indoor environment. In the Rural-Suburban mobile environment with elevation angles greater than 20 deg, multipath components from the satellite signal are 15-20 dB below the line-of-sight signal level and often originate from nearby reflectors. Thus shadowing is the dominant signal impairment and fading effects are again found to be relatively flat for a large fading margin. Because receiver motion induces rapid variations in the signal level, temporal diversity techniques such as interleaving, channel coding and retransmission can be used to combat short intermittent fading events. Antenna diversity and directivity techniques are again useful in this environment. Finally, in the Urban mobile environment, slower vehicle speeds and blockage by buildings causes signal fades that are too long and too deep to combat with signal margin or time diversity. Land-based signal boosters are needed to fill in the coverage gaps of the satellite only broadcast scheme. On frequency boosters are suggested to conserve bandwidth yet these

  9. Teaching braille line tracking using stimulus fading.

    PubMed

    Scheithauer, Mindy C; Tiger, Jeffrey H

    2014-01-01

    Line tracking is a prerequisite skill for braille literacy that involves moving one's finger horizontally across a line of braille text and identifying when a line ends so the reader may reset his or her finger on the subsequent line. Current procedures for teaching line tracking are incomplete, because they focus on tracking lines with only small gaps between characters. The current study extended previous line-tracking instruction using stimulus fading to teach tracking across larger gaps. After instruction, all participants showed improvement in line tracking, and 2 of 3 participants met mastery criteria for tracking across extended spaces.

  10. T1 VSAT Fade Compensation Statistical Results

    NASA Technical Reports Server (NTRS)

    Johnson, Sandra K.; Acosta, Roberto; Ugweje, Oke

    2000-01-01

    New satellite communication systems are steadily seeking to use higher frequency bands to accommodate the requirements for additional capacity. At these higher frequencies, propagation impairments that did not significantly affect the signal at lower frequencies begin to have considerable impact. In Ka-band. the next logical commercial frequency band to be used for satellite communication, attenuation of the signal due to rain is a primary concern. An experimental satellite built by NASA, the Advanced Communication Technology Satellite (ACTS). launched in September 1993, is the first U.S. communication satellite operating in the Ka-band. In addition to higher carrier frequencies, a number of other new technologies, including on-board baseband processing. multiple beam antennas, and rain fade detection and compensation techniques, were designed into the ACTS. Verification experiments have been conducted since the launch to characterize the new technologies. The focus of this paper is to characterize the method used by the ACTS TI Very Small Aperture Terminal (TI VSAT) ground stations in detecting the presence of fade in the communication signal and to adaptively compensate for it by the addition of burst rate reduction and forward error correction. Measured data obtained from the ACTS program was used to validate the compensation technique. A software process was developed and demonstrated to statistically characterize the increased availability achieved by the compensation techniques in terms of the bit error rate time enhancement factor. Several improvements to the ACTS technique are discussed and possible implementations for future Ka band system are offered.

  11. Autonomous detection of ISO fade point with color laser printers

    NASA Astrophysics Data System (ADS)

    Yan, Ni; Maggard, Eric; Fothergill, Roberta; Jessome, Renee J.; Allebach, Jan P.

    2015-01-01

    Image quality assessment is a very important field in image processing. Human observation is slow and subjective, it also requires strict environment setup for the psychological test 1. Thus developing algorithms to match desired human experiments is always in need. Many studies have focused on detecting the fading phenomenon after the materials are printed, that is to monitor the persistence of the color ink 2-4. However, fading is also a common artifact produced by printing systems when the cartridges run low. We want to develop an automatic system to monitor cartridge life and report fading defects when they appear. In this paper, we first describe a psychological experiment that studies the human perspective on printed fading pages. Then we propose an algorithm based on Color Space Projection and K-means clustering to predict the visibility of fading defects. At last, we integrate the psychological experiment result with our algorithm to give a machine learning tool that monitors cartridge life.

  12. A laboratory system for the investigation of rain fade compensation techniques for Ka-band satellites

    NASA Technical Reports Server (NTRS)

    Svoboda, James S.; Kachmar, Brian A.

    1993-01-01

    The design and performance of a rain fade simulation/counteraction system on a laboratory simulated 30/20 GHz, time division multiple access (TDMA) satellite communications testbed is evaluated. Severe rain attenuation of electromagnetic radiation at 30/20 GHz occurs due to the carrier wavelength approaching the water droplet size. Rain in the downlink path lowers the signal power present at the receiver, resulting in a higher number of bit errors induced in the digital ground terminal. The laboratory simulation performed at NASA Lewis Research Center uses a programmable PIN diode attenuator to simulate 20 GHz satellite downlink geographic rain fade profiles. A computer based network control system monitors the downlink power and informs the network of any power threshold violations, which then prompts the network to issue commands that temporarily increase the gain of the satellite based traveling wave tube (TWT) amplifier. After the rain subsides, the network returns the TWT to the normal energy conserving power mode. Bit error rate (BER) data taken at the receiving ground terminal serves as a measure of the severity of rain degradation, and also evaluates the extent to which the network can improve the faded channel.

  13. KIC 8462852 Faded throughout the Kepler Mission

    NASA Astrophysics Data System (ADS)

    Montet, Benjamin T.; Simon, Joshua D.

    2016-10-01

    KIC 8462852 is a superficially ordinary main sequence F star for which Kepler detected an unusual series of brief dimming events. We obtain accurate relative photometry of KIC 8462852 from the Kepler full-frame images, finding that the brightness of KIC 8462852 monotonically decreased over the four years it was observed by Kepler. Over the first ∼1000 days KIC 8462852 faded approximately linearly at a rate of 0.341 ± 0.041% yr‑1, for a total decline of 0.9%. KIC 8462852 then dimmed much more rapidly in the next ∼200 days, with its flux dropping by more than 2%. For the final ∼200 days of Kepler photometry the magnitude remained approximately constant, although the data are also consistent with the decline rate measured for the first 2.7 years. Of a sample of 193 nearby comparison stars and 355 stars with similar stellar parameters, none exhibit the rapid decline by >2% or the cumulative fading by 3% of KIC 8462852. Moreover, of these comparison stars, only one changes brightness as quickly as the 0.341% yr‑1 measured for KIC 8462852 during the first three years of the Kepler mission. We examine whether the rapid decline could be caused by a cloud of transiting circumstellar material, finding that while such a cloud could evade detection in submillimeter observations, the transit ingress and duration cannot be explained by a simple cloud model. Moreover, this model cannot account for the observed longer-term dimming. No known or proposed stellar phenomena can fully explain all aspects of the observed light curve.

  14. Radar prediction of absolute rain fade distributions for earth-satellite paths and general methods for extrapolation of fade statistics to other locations

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1982-01-01

    The first absolute rain fade distribution method described establishes absolute fade statistics at a given site by means of a sampled radar data base. The second method extrapolates absolute fade statistics from one location to another, given simultaneously measured fade and rain rate statistics at the former. Both methods employ similar conditional fade statistic concepts and long term rain rate distributions. Probability deviations in the 2-19% range, with an 11% average, were obtained upon comparison of measured and predicted levels at given attenuations. The extrapolation of fade distributions to other locations at 28 GHz showed very good agreement with measured data at three sites located in the continental temperate region.

  15. OVERVIEW OF SPILLWAY FROM SOUTH BANK OF RIVER; FADING NORTHNORTHEAST ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OVERVIEW OF SPILLWAY FROM SOUTH BANK OF RIVER; FADING NORTH-NORTHEAST - Shoshone Falls Hydroelectric Project, Reservoir and Dam Complex, North Bank of Snake River, extreme Eastern end of the Shoshone Falls Hydroelectric Project, Tipperary Corner, Jerome County, ID

  16. NiH2 capacity fade during early cycling

    NASA Technical Reports Server (NTRS)

    Zagrodnik, Jeffrey P.

    1993-01-01

    Tests were conducted on nickel hydrogen batteries to determine the charge efficiency of the nickel electrode as a function of rate and temperature, cell discharge capacity, and capacity fade. Test procedures and results are presented in outline and graphic form.

  17. An Automated Fading Procedure to Alter Sexual Responsiveness in Pedophiles

    ERIC Educational Resources Information Center

    Laws, D. R.; Pawlowski, A. V.

    1975-01-01

    An automated stimulus fading procedure was used to strengthen sexual responsiveness to adult stimuli in two pedophiles. The degree of responsiveness was indicated by changes in the penile response. Implications for future research are discussed. (Author)

  18. Combining stimulus fading, reinforcement, and extinction to treat food refusal.

    PubMed

    Freeman, K A; Piazza, C C

    1998-01-01

    The food refusal of a 6-year-old girl with destructive behavior was treated using stimulus fading, reinforcement, and escape extinction. Intake increased and compliance with prompting procedures remained relatively stable despite the increased consumption requirement.

  19. Kinetics of the Fading of Phenolphthalein in Alkaline Solution.

    ERIC Educational Resources Information Center

    Nicholson, Lois

    1989-01-01

    Described is an experiment which illustrates pseudo-first-order kinetics in the fading of a common indicator in an alkaline solution. Included are background information, details of materials used, laboratory procedures, and sample results. (CW)

  20. Fading of Jupiter's South Equatorial Belt

    NASA Technical Reports Server (NTRS)

    Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma

    2011-01-01

    One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.

  1. Optically derived elevation angle dependence of fading for satellite PCS

    NASA Technical Reports Server (NTRS)

    Akturan, R.; Vogel, Wolf J.

    1995-01-01

    Images of urban Japan taken vertically through a 180 deg fisheye lens were analyzed to derive, as a function of elevation the fraction of sky that is clear, shadowed by trees, or blocked by buildings. At 32 deg elevation, results match those derived from satellite measurements fit to a 3-state fade model. Using the same model, for the first time the elevation angle dependence of mobile satellite fading is predicted.

  2. Tetanic fade following administration of nondepolarizing neuromuscular blocking drugs.

    PubMed

    Gibson, F M; Mirakhur, R K

    1989-06-01

    Fade in response to tetanic stimulation was studied following administration of atracurium 120 or 225 micrograms/kg, vecuronium 23 or 40 micrograms/kg, pancuronium 30 or 60 micrograms/kg, or d-tubocurarine 185 or 450 micrograms/kg. Ten patients received each dose and tetanic fade was measured at maximum block in the patients, who received the lower doses of the relaxants or at 10% recovery in those who received the higher doses. Fade during tetanic stimulation was generally similar in all the groups with the exception of the higher dose of pancuronium which showed a significantly greater fade in comparison with the higher doses of atracurium and d-tubocurarine. If fade in response to tetanic stimulation represents a prejunctional effect, the results from the present study suggest that neuromuscular blocking drugs cannot be differentiated with respect to their relative prejunctional effects by measurement of tetanic fade during established block after administration of clinically useful doses as used in the present study.

  3. Attentional model for the effectiveness of fading in training reading- vocabulary with retarded persons.

    PubMed

    Dorry, G W

    1976-11-01

    Researchers have shown that a simple reading-vocabulary can be trained by repeatedly pairing picture and word and that fading the picture over trials increases the efficiency of training. An attention hypothesis attributes the effectiveness of fading to an increase in attention to the word caused by the fading out of the picture. In an alternative hypothesis, stimulus change, it is proposed that the mechanism of fading derives from the increased salience of the changing stimuli, so that fading in the word would be as effective as fading out the picture. These competing hypotheses were tested by training 48 nonreading retarded persons (in four equated groups) under the following conditions: fade picture out, fade word in, double fade (picture fades out and word fades in simultaneously), and standard (picture and word paired without fading). Tests of vocabulary-learning showed that the fade picture out and double-fade conditions were equally effective and superior to the standard and fade word in conditions, which were equally ineffective. These findings were inconsistent with the stimulus-change hypothesis, but consistent with a two-look attentional model, based on the Zeaman and House attention theory (1963).

  4. Performance evaluation of land mobile satellite system under fading and interference using multiple TCM by Monte-Carlo simulation

    NASA Technical Reports Server (NTRS)

    Kwa, S. C.; Vanderaar, Mark J.; Kim, Junghwan; Stevens, Grady H.

    1991-01-01

    The performance of the land mobile satellite system (LMSS) was evaluated by using two trellis coded modulation (TCM) schemes under multipath fading and interference. The results were also compared with uncoded QPSK. The trellis coding formats included a trellis code designed for optimum performance on the fading channel that typifies satellite to mobile communications, as well as one designed for optimum performance in the additive white Gaussian noise (AWGN) channel. The results show that, in Rayleigh fading, the TCM code designed for optimum performance in such an environment performs 4 dB better than the TCM code designed for optimum performance in AWGN, and 10 dB better than the uncoded format, at a bit error rate (BER) of 10 exp -4. Additional results on the performance degradation due to the nonlinearities in the satellite transponder and the adjacent and cochannel interference show that the TCM system is more sensitive than the uncoded system to the phase distortion caused by these impairments.

  5. The land mobile satellite communication channel - Recording, statistics, and channel model

    NASA Astrophysics Data System (ADS)

    Lutz, Erich; Cygan, Daniel; Dippold, Michael; Dolainsky, Frank; Papke, Wolfgang

    1991-05-01

    The communication channel between the MARECS satellite at 26 deg W and a cruising van was measured and recorded in European areas exhibiting satellite elevations from 13 to 43 deg. Different environments and mobile antennas were tested. Results of an extensive statistical evaluation include spectra of the fading amplitude, probability density, and distribution of the received signal power as well as the percentage of time for fade and nonfade periods. Based on the physical phenomena of multipath fading and signal shadowing, an analog model of the land mobile satellite channel which can readily be used for software and hardware fading simulation is developed. The most important parameter of this model is the time-share of shadowing, A, ranging from less than 1 percent on southern highways to 89 percent in the city of Stockholm. The Rice factor, c, which characterizes the channel during unshadowed periods, can vary from 3.9 to 18.1 dB. For analytical purposes, the land mobile satellite channel can be represented by a digital two-state Gilbert-Elliott model. For DPSK (differential phase-shift keying) modulation with a 10-dB signal-to-noise ratio in the satellite link, the mean bit error probability in the unshadowed channel state is typically in the range of 0.0001-0.01, while it is around 0.3 in the shadowed channel state. With regard to data transmission, block error probability density, error gap distribution, and block error probability are discussed.

  6. Rain Fade Compensation for Ka-Band Communications Satellites

    NASA Technical Reports Server (NTRS)

    Mitchell, W. Carl; Nguyen, Lan; Dissanayake, Asoka; Markey, Brian; Le, Anh

    1997-01-01

    This report provides a review and evaluation of rain fade measurement and compensation techniques for Ka-band satellite systems. This report includes a description of and cost estimates for performing three rain fade measurement and compensation experiments. The first experiment deals with rain fade measurement techniques while the second one covers the rain fade compensation techniques. The third experiment addresses a feedback flow control technique for the ABR service (for ATM-based traffic). The following conclusions were observed in this report; a sufficient system signal margin should be allocated for all carriers in a network, that is a fixed clear-sky margin should be typically in the range of 4-5 dB and should be more like 15 dB in the up link for moderate and heavy rain zones; to obtain a higher system margin it is desirable to combine the uplink power control technique with the technique that implements the source information rate and FEC code rate changes resulting in a 4-5 dB increase in the dynamic part of the system margin. The experiments would assess the feasibility of the fade measurements and compensation techniques, and ABR feedback control technique.

  7. Autonomous detection of text fade point with color laser printers

    NASA Astrophysics Data System (ADS)

    Ju, Yanling; Maggard, Eric; Jessome, Renee; Allebach, Jan

    2015-01-01

    Fading is one of the issues of most critical concern for print quality degradation with color laser electro- photographic printers. Fading occurs when the cartridge is depleted. ISO/IEC 19798:2007(E) specifies a process for determining the cartridge page yield for a given color electro-photographic printer model. It is based on repeatedly printing a suite of test pages, followed by visual examination of the sequence of printed diagnostic pages. But this method is a very costly process since it involves visual examination of a large number of pages. And also the final decision is based on the visual examination of a specially designed diagnostic page, which is different than typical office document pages, since it consists of color bars, and contains no text. In this paper, we propose a new method to autonomously detect the text fading in prints from home or office color printers using a typical office document page instead of a specially designed diagnostic page. In our method, we scan and analyze the printed pages to predict where expert observers would judge fading to have occurred in the print sequence. Our approach is based on a machine-learning framework in which features derived from image analysis are mapped to a fade point prediction.

  8. Measurement of multipath delay profile in land mobile satellite channels

    NASA Technical Reports Server (NTRS)

    Ikegami, Tetsushi; Arakaki, Yoshiya; Wakana, Hiromitsu; Suzuki, Ryutaro

    1993-01-01

    Mobile satellite communication channel has been evaluated mainly with fading statistics of signal. When bandwidth of transmitting signal becomes wider, frequency selectivity of fading becomes a significant factor of the channel. Channel characteristics, not only signal variation but multipath delay spread should be evaluated. A multipath measurement system is proposed and developed for mobile satellite applications. With this system and ETS-V satellite, multipath delay profiles are measured in various environments including Tokyo metropolis and Sapporo city at 1.5 GHz. Results show that the maximum excess delay is within 1 microsec and the maximum delay spread is 0.2 microsecs at elevation angles of 40 to 47 degrees. In wideband signal transmission of about 1 MHz and more, designers should consider the effect of selective fading due to the multipath of land mobile satellite channel.

  9. Stochastic Wireless Channel Modeling, Estimation and Identification from Measurements

    SciTech Connect

    Olama, Mohammed M; Djouadi, Seddik M; Li, Yanyan

    2008-07-01

    This paper is concerned with stochastic modeling of wireless fading channels, parameter estimation, and system identification from measurement data. Wireless channels are represented by stochastic state-space form, whose parameters and state variables are estimated using the expectation maximization algorithm and Kalman filtering, respectively. The latter are carried out solely from received signal measurements. These algorithms estimate the channel inphase and quadrature components and identify the channel parameters recursively. The proposed algorithm is tested using measurement data, and the results are presented.

  10. Transmission over EHF mobile satellite channels

    NASA Technical Reports Server (NTRS)

    Zhuang, W.; Chouinard, J.-Y.; Yongacoglu, A.

    1993-01-01

    Land mobile satellite communications at Ka-band (30/20 GHz) are attracting an increasing interest among researchers because of the frequency band availability and the possibility of small earth station designs. However, communications at the Ka-band pose significant challenges in the system designs due to severe channel impairments. Because only very limited experimental data for mobile applications at Ka-band is available, this paper studies the channel characteristics based on experimental data at L-band (1.6/1.5 GHz) and the use of frequency scaling. The land mobile satellite communication channel at Ka-band is modelled as log-normal Rayleigh fading channel. The first and second-order statistics of the fading channel are studied. The performance of a coherent BPSK system over the fading channel at L-band and K-band is evaluated theoretically and validated by computer simulations. Conclusions on the communication channel characteristics and system performance at L-band and Ka-band are presented.

  11. Fast Faraday fading of long range satellite signals.

    NASA Technical Reports Server (NTRS)

    Heron, M. L.

    1972-01-01

    20 MHz radio signals have been received during the day from satellite Beacon-B when it was below the optical horizon by using a bank of narrow filters to improve the signal to noise ratio. The Faraday fading rate becomes constant, under these conditions, at a level determined by the plasma frequency just below the F-layer peak. Variations in the Faraday fading rate reveal fluctuations in the electron density near the peak, while the rate of attaining the constant level depends on the shape of the electron density profile.

  12. An analysis of vocal stereotypy and therapist fading.

    PubMed

    Athens, Elizabeth S; Vollmer, Timothy R; Sloman, Kimberly N; St Peter Pipkin, Claire

    2008-01-01

    A functional analysis for a boy with Down syndrome and autism suggested that vocal stereotypy was maintained by automatic reinforcement. The analysis also showed that instructions and noncontingent attention suppressed vocal stereotypy. A treatment package consisting of noncontingent attention, contingent demands, and response cost effectively reduced vocal stereotypy. The treatment package remained effective even when noncontingent attention was removed, making the procedure easier to implement. Also, the presence of the therapist in the room with the participant was faded systematically. After completion of fading, vocal stereotypy remained low during conditions similar to the no-consequence phase of the functional analysis. PMID:18595296

  13. Nanoscale Surface Modification of Lithium-Rich Layered-Oxide Composite Cathodes for Suppressing Voltage Fade.

    PubMed

    Zheng, Fenghua; Yang, Chenghao; Xiong, Xunhui; Xiong, Jiawen; Hu, Renzong; Chen, Yu; Liu, Meilin

    2015-10-26

    Lithium-rich layered oxides are promising cathode materials for lithium-ion batteries and exhibit a high reversible capacity exceeding 250 mAh g(-1) . However, voltage fade is the major problem that needs to be overcome before they can find practical applications. Here, Li1.2 Mn0.54 Ni0.13 Co0.13 O2 (LLMO) oxides are subjected to nanoscale LiFePO4 (LFP) surface modification. The resulting materials combine the advantages of both bulk doping and surface coating as the LLMO crystal structure is stabilized through cationic doping, and the LLMO cathode materials are protected from corrosion induced by organic electrolytes. An LLMO cathode modified with 5 wt % LFP (LLMO-LFP5) demonstrated suppressed voltage fade and a discharge capacity of 282.8 mAh g(-1) at 0.1 C with a capacity retention of 98.1 % after 120 cycles. Moreover, the nanoscale LFP layers incorporated into the LLMO surfaces can effectively maintain the lithium-ion and charge transport channels, and the LLMO-LFP5 cathode demonstrated an excellent rate capacity.

  14. Convolutional code performance in planetary entry channels

    NASA Technical Reports Server (NTRS)

    Modestino, J. W.

    1974-01-01

    The planetary entry channel is modeled for communication purposes representing turbulent atmospheric scattering effects. The performance of short and long constraint length convolutional codes is investigated in conjunction with coherent BPSK modulation and Viterbi maximum likelihood decoding. Algorithms for sequential decoding are studied in terms of computation and/or storage requirements as a function of the fading channel parameters. The performance of the coded coherent BPSK system is compared with the coded incoherent MFSK system. Results indicate that: some degree of interleaving is required to combat time correlated fading of channel; only modest amounts of interleaving are required to approach performance of memoryless channel; additional propagational results are required on the phase perturbation process; and the incoherent MFSK system is superior when phase tracking errors are considered.

  15. Fade Measurements into Buildings from 500 to 3000 MHz

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1996-01-01

    Slant-path fade measurements from 500 to 3000 MHz were made into six different buildings employing a vector network analyzer, a tower-mounted transmitting antenna and an automatically positioned receiving antenna. The objective of the measurements was to provide information for satellite audio broadcasting and personal communications satellite design on the correlation of fading inside buildings. Fades were measured with 5 cm spatial separation and every 0.2 percent of the frequency. Median fades ranged from 10 to 20 dB in woodframe houses with metal roofs and walls without and with an aluminum heat shield, respectively. The median decorrelation distance was from 0.5 to 1.1. m and was independent of frequency. The attenuation into the buildings increased only moderately with frequency in most of the buildings with a median slope of about 1 to 3 db/GHz, but increased fastest in the least attenuating building with a slope of 5 dB/GHz. The median decorrelation bandwidth ranged from 1.2 to 3.8 percent of frequency in five of the buildings, and was largest in the least attenuating building, with 20.2 percent of frequency.

  16. Fade Measurements into Buildings from 500 to 3000 MHz

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1996-01-01

    Slant-path fade measurements from 500 to 3000 MHz were made into six different buildings employing a vector network analyzer, a tower-mounted transmitting antenna and an automatically positioned receiving antenna. The objective of the measurements was to provide information for satellite audio broadcasting and personal communications satellite design on the correlation of fading inside buildings. Fades were measured with 5 cm spatial separation and every 0.2% of the frequency. Median fades ranged from 10 to 20 dB in woodframe houses with metal roofs and walls without and with an aluminum heatshield, respectively. The median decorrelation distance was from 0.5 to 1.1 m and was independent of frequency. The attenuation into the buildings increased only moderately with frequency in most of the buildings with a median slope of about 1 to 3 dB/GHz, but increased fastest in the least attenuating building with a slope of 5 dB/GHz. The median decorrelation bandwidth ranged from 1.2 to 3.8% of frequency in five of the buildings, and was largest in the least attenuating building, with 20.2% of frequency.

  17. Treating Total Liquid Refusal with Backward Chaining and Fading.

    ERIC Educational Resources Information Center

    Hagopian, Louis P.; And Others

    1996-01-01

    In this study of a 12-year-old boy with autism, mental retardation, and a history of severe gastrointestinal problems, who refused liquids and food, backward chaining was used to shape drinking from a cup and a fading procedure was used to increase the water he was required to drink. (Author/CR)

  18. Enuresis Control through Fading, Escape, and Avoidance Training.

    ERIC Educational Resources Information Center

    Hansen, Gordon D.

    1979-01-01

    A twin signal device that provides both escape and avoidance conditioning in enuresis control was documented with case studies of two enuretic children (eight and nine years old). In addition, a technique of fading as an adjunct to the process was utilized with one subject. (Author/SBH)

  19. Use of Texture Fading in the Treatment of Food Selectivity.

    ERIC Educational Resources Information Center

    Shore, Bridget A.; Babbitt, Roberta L.; Williams, Keith E.; Coe, David A.; Snyder, Angela

    1998-01-01

    A study investigated the efficacy of texture fading in the treatment of food selectivity displayed by four children (ages 2-5). Successful treatment involved the gradual addition of higher textures based on results of periodic probes. Food acceptance and swallowing were reinforced, while food refusal and expulsion were placed on extinction.…

  20. A Probe Intermix Procedure for Fading Response Prompts.

    ERIC Educational Resources Information Center

    Billingsley, Felix F.

    1987-01-01

    A prompt fading method was employed to teach an eight-year-old student with severe behavior disorders the self-paced use of a functional behavior (requesting rather than grabbing food items). Initial pairing of prompts and natural cues was followed by a mix of prompted and probe (unprompted) trials. (Author/JW)

  1. The Landmark Decision that Faded into Historical Obscurity

    ERIC Educational Resources Information Center

    Nance, Molly

    2007-01-01

    This article takes a look at the Mendez v. Westminster School District, a landmark case that faded into historical obscurity. In the 1940s, Gonzalo and Felicita Mendez wanted their three children to attend the school nearest their farm, which was the 17th Street Elementary School in Westminster. But in the Westminster, Orange County, El Medina,…

  2. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    NASA Technical Reports Server (NTRS)

    Kavak, Adnan; Xu, Guanghan; Vogel, W. J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, global positioning system (GPS) receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  3. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    NASA Technical Reports Server (NTRS)

    Kavak, Adnan; Xu, Guang-Han; Vogel, Wolfhard J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, GPS receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  4. Probability of error analysis for FHSS/CDMA communications in the presence of fading

    NASA Astrophysics Data System (ADS)

    Wickert, Mark A.; Turcotte, Randy L.

    1992-04-01

    Expressions are found for the error probability of a slow frequency-hopped spread-spectrum (FHSS) M-ary FSK multiple-access system in the presence of slow-nonselective Rayleigh or single-term Rician fading. The approach is general enough to allow for the consideration of independent power levels; that is to say, the power levels of the interfering signals can be varied with respect to the power level of the desired signal. The exact analysis is carried out for one and two multiple-access interferers using BFSK modulation. The analysis is general enough for the consideration of the near/far problem under the specified channel conditions. Comparisons between the error expressions developed here and previously published upper bounds (Geraniotis and Pursley, 1982) show that, under certain conditions, the previous upper bounds on the error probability may exceed the true error probability by an order of magnitude.

  5. Comparative study on the performance of power and bandwidth efficient modulations in LMSS under fading and interference

    NASA Technical Reports Server (NTRS)

    Liu, Jian; Kim, Junghwan; Kwatra, S. C.; Stevens, Grady H.

    1991-01-01

    Aspects of error performance of various power and bandwidth efficient modulations for the land mobile satellite systems (LMSS) were investigated under multipath fading and interferences by using Monte-Carlo simulation. A differential detection for 16QAM (quadrature amplitude modulation) was proposed to cope with Ricean fading and Doppler shift. Computer simulation results show that the performance of 16QAM with differential detection is as good as that of 16PSK with coherent detection and 3 dB better than that of 16PSK with differential detection, although it degrades by about 4.5 dB as compared to 16QAM with coherent detection under an additive white Gaussian noise (AWGN) channel. For the nonlinear channels, 16QAM with modified signal constellations is introduced and analyzed. The simulation results show that the modified 16QAM exhibits a gain of 2.5 dB over 16PSK under traveling-wave tube nonlinearity, and about 4 dB gain over 16PSK at the bit error rate of 10 exp -5 under AWGN. Computer simulation results for modified 16 QAM under cochannel interference and adjacent-channel interference are also presented.

  6. Exact probability of error analysis for FHSS/CDMA communications in the presence of single term Rician fading

    NASA Astrophysics Data System (ADS)

    Turcotte, Randy L.; Wickert, Mark A.

    An exact expression is found for the probability of bit error of an FHSS-BFSK (frequency-hopping spread-spectrum/binary-frequency-shift-keying) multiple-access system in the presence of slow, nonselective, 'single-term' Rician fading. The effects of multiple-access interference and/or continuous tone jamming are considered. Comparisons are made between the error expressions developed here and previously published upper bounds. It is found that under certain channel conditions the upper bounds on the probability of bit error may exceed the actual probability of error by an order of magnitude.

  7. Channel estimation in DCT-based OFDM.

    PubMed

    Wang, Yulin; Zhang, Gengxin; Xie, Zhidong; Hu, Jing

    2014-01-01

    This paper derives the channel estimation of a discrete cosine transform-(DCT-) based orthogonal frequency-division multiplexing (OFDM) system over a frequency-selective multipath fading channel. Channel estimation has been proved to improve system throughput and performance by allowing for coherent demodulation. Pilot-aided methods are traditionally used to learn the channel response. Least square (LS) and mean square error estimators (MMSE) are investigated. We also study a compressed sensing (CS) based channel estimation, which takes the sparse property of wireless channel into account. Simulation results have shown that the CS based channel estimation is expected to have better performance than LS. However MMSE can achieve optimal performance because of prior knowledge of the channel statistic.

  8. Motor learning with fading and growing haptic guidance.

    PubMed

    Heuer, Herbert; Lüttgen, Jenna

    2014-07-01

    Haptic guidance has been shown to have both facilitatory and interfering effects on motor learning. Interfering effects have been hypothesized to result from the particular dynamic environment, which supports a passive role of the learner, and they should be attenuated by fading guidance. Facilitatory effects, in particular for dynamic movement characteristics, have been hypothesized to result from the high-quality information provided by haptic demonstration. If haptic demonstration provides particularly precise information about target movements, the motor system's need for such information should more likely increase in the course of motor learning, in which case growing guidance should be more beneficial for learning. We contrasted fading and growing guidance in the course of learning a spatio-temporal motor pattern. To stimulate an active role of the learner, practice trials consisted of three phases, a visual demonstration of the target movement, a guided reproduction, and a reproduction without haptic guidance. Performance was assessed in terms of variable duration errors, relative-timing errors, variable path-length errors, and shape errors. Motor learning with growing and fading guidance turned out to be largely equivalent, so that the notion of an increasing optimal precision of haptic demonstrations, which matches a demand of increasingly precise information on the target movement, found no support. Duration errors declined only with fading, but not with growing guidance. Relative timing revealed a benefit of immediately preceding haptic demonstration, but learning was not different between the two practice protocols. This contrast between absolute and relative timing adds to other evidence according to which acquisition of these two aspects of motor timing involves different learning mechanisms. Whereas relative timing gained from immediately preceding haptic demonstration, but revealed no practice-related improvement in the presence of haptic guidance

  9. On the nature of rapidly fading Type II supernovae

    NASA Astrophysics Data System (ADS)

    Moriya, Takashi J.; Pruzhinskaya, Maria V.; Ergon, Mattias; Blinnikov, Sergei I.

    2016-01-01

    It has been suggested that Type II supernovae with rapidly fading light curves (a.k.a. Type IIL supernovae) are explosions of progenitors with low-mass hydrogen-rich envelopes which are of the order of 1 M⊙. We investigate light-curve properties of supernovae from such progenitors. We confirm that such progenitors lead to rapidly fading Type II supernovae. We find that the luminosity of supernovae from such progenitors with the canonical explosion energy of 1051 erg and 56Ni mass of 0.05 M⊙ can increase temporarily shortly before all the hydrogen in the envelope recombines. As a result, a bump appears in their light curves. The bump appears because the heating from the nuclear decay of 56Ni can keep the bottom of hydrogen-rich layers in the ejecta ionized, and thus the photosphere can stay there for a while. We find that the light-curve bump becomes less significant when we make explosion energy larger (≳2 × 1051 erg), 56Ni mass smaller (≲0.01 M⊙), 56Ni mixed in the ejecta, or the progenitor radius larger. Helium mixing in hydrogen-rich layers makes the light-curve decline rates large but does not help reducing the light-curve bump. Because the light-curve bump we found in our light-curve models has not been observed in rapidly fading Type II supernovae, they may be characterized by not only low-mass hydrogen-rich envelopes but also higher explosion energy, larger degrees of 56Ni mixing, and/or larger progenitor radii than slowly fading Type II supernovae, so that the light-curve bump does not become significant.

  10. Optical communication system performance with tracking error induced signal fading.

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.; Premo, D. A.

    1973-01-01

    System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming (1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and (2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2- to 3-dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.

  11. Land-mobile-satellite fade measurements in Australia

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius; Hase, Yoshihiro

    1992-01-01

    Attenuation measurements were implemented at L-band (1.5 GHz) in southeastern Australia during an 11-day period in October 1988 as part of a continuing examination of the propagation effects due to roadside trees and terrain for mobile-satellite service. Beacon transmissions from the geostationary ETS-V and IPORS satellites were observed. The Australian campaign expanded to another continent our Mobile Satellite Service data base of measurements executed in the eastern and southwestern United States regions. An empirical fade distribution model based on U.S. data predicted the Australian results with errors generally less than 1 dB in the 1-20 percent probability region. Directive antennas are shown to suffer deeper fades under severe shadowing conditions (3 dB excess at 4 percent), the equal-probability isolation between co- and cross-polarized transmissions deteriorated to 10 dB at the 5 dB fade level, and antenna diversity reception may reduce unavailability of the system by a factor of 2-8.

  12. Rain Fade Compensation Alternatives for Ka Band Communication Satellites

    NASA Technical Reports Server (NTRS)

    Acosta, Roberto J.

    1997-01-01

    Future satellite communications systems operating in Ka-band frequency band are subject to degradation produced by the troposphere which is much more severe than those found at lower frequency bands. These impairments include signal absorption by rain, clouds and gases, and amplitude scintillation's arising from refractive index irregularities. For example, rain attenuation at 20 GHz is almost three times that at 11 GHz. Although some of these impairments can be overcome by oversizing the ground station antennas and high power amplifiers, the current trend is using small (less than 20 inches apertures), low-cost ground stations (less than $1000) that can be easily deployed at user premises. As a consequence, most Ka-band systems are expected to employ different forms of fade mitigation that can be implemented relatively easily and at modest cost. The rain fade mitigation approaches are defined by three types of Ka-band communications systems - a low service rate (less than 1.5 Mb/s), a moderate service rate (1.5 to 6 Mb/s) system and a high service rate (greater than 43 Mb/s) system. The ACTS VSAT network, which includes an adaptive rain fade technique, is an example of a moderate service rate.

  13. Fade of the responses of the isolated, blood-perfused dog atrium to cholinergic interventions.

    PubMed

    Furukawa, Y; Martin, P; Levy, M N

    1984-05-01

    In the isolated, blood-perfused, canine right atrium, intramural parasympathetic nerve stimulation and intra-arterial infusions of acetylcholine induced substantial negative chronotropic and inotropic responses. The responses to parasympathetic stimulation reached their maximum values quickly, and then usually faded back toward control levels over the next 1 or 2 min of stimulation. The fade of the responses at high stimulation frequencies (greater than or equal to 30 Hz) was significantly greater than that at lower frequencies. The inotropic responses to acetylcholine infusion (1 microgram/min) faded slightly but significantly, whereas the chronotropic responses did not fade at all. These results suggest that the fade of the cardiac responses to parasympathetic stimulation is mainly ascribable to a progressive reduction in the rate of acetylcholine release from the nerve endings, especially at higher stimulation frequencies. The fade of the inotropic responses was more pronounced and had a longer time course than that of the chronotropic responses. Furthermore, the fade of the inotropic responses diminished significantly as the response magnitude was augmented by an increase in stimulation voltage. Conversely, the fade of chronotropic responses was not significantly affected by this intervention. These differences in the inotropic and chronotropic responses to neural stimulation, and the occurrence of a slight fade of the inotropic response to acetylcholine infusion, suggest that in addition to the predominant prejunctional mechanism, a postjunctional phenomenon may also be partly responsible for the fade of the inotropic response to cholinergic interventions.

  14. Dual-pilot tone calibration technique. [to reduce multipath fading effects at mobile satellite link receiver

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K.

    1986-01-01

    Pilot-based calibration techniques are used to reduce the effects of multipath fading in mobile satellite receivers. One of the more recent of these techniques, namely the tone calibration technique (TCT), suggests transmitting double sideband modulation with the pilot tone located at the center of its spectrum where the amplitude and phase characteristics of the channel are most stable. To 'make room' for the pilot in the presence of the Doppler shift, the equivalent low-pass data sidebands must be shaped so as to have zero response in the neighborhood of dc. Other techniques such as transparent tone-in-band (TTIB) similarly 'notch out' a hole in the center of the data spectrum for location of the pilot. An alternate possibility which is at the same time much more bandwidth efficient than TCT is a dual-pilot tone calibration technique (DPTCT) that symmetrically locates a pair of pilots outside the data spectrum near the band edges of the channel. The operation and performance of DPTCT are analyzed, and its effectiveness is compared to that of the single tone TCT technique.

  15. Train-of-four fade during onset of neuromuscular block with nondepolarising neuromuscular blocking agents.

    PubMed

    Gibson, F M; Mirakhur, R K

    1989-04-01

    Fade in the train-of-four (TOF) responses during onset of neuromuscular block was studied following administration of atracurium (225 or 450 micrograms/kg), vecuronium (40 or 80 micrograms/kg), pancuronium (60 or 120 micrograms/kg) and tubocurarine (450 micrograms/kg). TOF ratios were measured at approximate heights of T1 (first response in the TOF) of 75, 50 and 25%. Fade in TOF increased as the height of T1 decreased, with maximum fade being observed at T1 of 25%. The greatest difference between relaxants was observed at T1 of 25%, vecuronium showing the least fade and pancuronium, atracurium and tubocurarine showing increasing fade, in that order. The difference between atracurium and tubocurarine or between vecuronium and pancuronium was not significant, but the degree of TOF fade was significantly greater with atracurium and tubocurarine in comparison to vecuronium or pancuronium.

  16. Multiyear slant-path rain fade statistics at 28.56 GHz for Wallops Island, Va.

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1980-01-01

    The multiyear rain fade statistics collected in the Wallops Island, Va., area at 28.56 GHz during 1977 through 1979 showed that the overall fade distributions for the individual years showed small differences. Exceedance time variations were observed in the monthly and time of day fade data from year to year, but the second year fades relative to the first year had less than 20% rms deviation. These results are useful to designers of earth-satellite communications systems which require reliable fade statistics for establishing link-margin requirements. The Wallops Island fade distribution had an rms decibel deviation of less than 14% when compared with the International Radio Consultative Committee prediction model.

  17. Rain-fade simulation and power augmentation for satellite communication systems

    NASA Technical Reports Server (NTRS)

    Shalkhauser, Kurt A.; Nagy, Lawrence A.; Svoboda, James S.

    1990-01-01

    The design and implementation of an automated rain-fade simulation and power augmentation system is presented. The system experimentally simulates and measures the effects of radiofrequency power fade on a 20 GHz communication link using a multimode travelling wave tube amplifier for loss compensation. Precision, computer-controlled attenuators are used in the fade simulation. Test plans for analog and digital testing are discussed.

  18. Channel simulation for direct-detection optical communication systems

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.

    1974-01-01

    A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct-detection optical communication system. The system is capable of providing signal fading statistics which obey log-normal, beta, Rayleigh, Ricean, or chi-square density functions. Experimental tests of the performance of the channel simulator are presented.

  19. Channel simulation for direct detection optical communication systems

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.

    1974-01-01

    A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct detection optical communication system. The system is capable of providing signal fading statistics which obey log normal, beta, Rayleigh, Ricean or chi-squared density functions. Experimental tests of the performance of the Channel Simulator are presented.

  20. Dye fading test for mission control operator console displays

    NASA Technical Reports Server (NTRS)

    Lockwood, H. E.

    1975-01-01

    A dye fading test of 40 days duration was conducted to determine the effect of mission control operator console and ambient lighting effects on a series of photographic products under consideration for use in mission console operator consoles. Six different display samples, each containing 36 windows of several different colors, were prepared and placed in the mission control consoles for testing. No significant changes were recorded during the testing period. All changes were attributed to a mechanical problem with the densitometer. Detailed results are given in graphs.

  1. Color transplant for reverse ageing of faded artworks

    NASA Astrophysics Data System (ADS)

    Del Mastio, A.; Piva, A.; Barni, M.; Cappellini, V.; Stefanini, L.

    2008-02-01

    Nowadays, photographs are one of the most used media for communication. Images are used for the representation of documents, Cultural goods, and so on: they are used to pass on a wedge of historical memory of the society. Since its origin, the photographic technique has got several improvements; nevertheless, photos are liable to several damages, both concerning the physical support and concerning the colors and figures which are depicted in it: for example, think about scratches or rips happened to a photo, or think about the fading or red (or yellow) toning concerning the colors of a photo. In this paper, we propose a novel method which is able to assess the original beauty of digital reproductions of aged photos, as well as digital reproductions of faded goods. The method is based on the comparison of the degraded image with a not-degraded one showing similar contents; thus, the colors of the not-degraded image can be transplanted in the degraded one. The key idea is a dualism between the analytical mechanics and the color theory: for each of the degraded and not-degraded images we compute first a scatter plot of the x and y normalized coordinates of their colors; these scatter diagrams can be regarded as a system of point masses, thus provided of inertia axes and an inertia ellipsoid. Moving the scatter diagram of the degraded image over the one belonging to the not-degraded image, the colors of the degraded image can be restored.

  2. Fade responses at neuroeffector junction to vagal stimulation in the isolated, blood-perfused dog atrium.

    PubMed

    Furukawa, Y; Saegusa, K; Ogiwara, Y; Chiba, S

    1988-01-01

    Effects of physostigmine and of beating rate on the negative chronotropic and inotropic responses to tonic intramural parasympathetic nerve stimulation at a frequency of 5 Hz for 2 min were investigated, using the isolated, blood-perfused dog atrium which was pretreated with propranolol. The responses to stimulation reached a maximum, and then "faded" back toward the control levels during stimulation. Before physostigmine, the fade of the inotropic response was consistently observed but the fade of the chronotropic response was minimal. Both the maximum effect and the fade of the chronotropic response were augmented dose-dependently by physostigmine in spontaneously beating atria. Physostigmine increased the maximum chronotropic response to infusion of acetylcholine (ACh) but did not potentiate the fade response. These results suggest that the potentiation of the fade of the chronotropic response to stimulation after physostigmine is due to decreases in the amount of ACh at the neuroeffector junction. The maximum negative inotropic responses were dose-dependently potentiated similarly by physostigmine in isolated spontaneously beating or paced atria. The fade of the inotropic response in spontaneously beating atria was decreased along with reduction of the rate by physostigmine, whereas the fades in paced atria at 2 and 3 Hz were not changed, showing that decreases in rate during stimulation influenced the reduction of the fade. Increases in contractile force induced by infusion of CaCl2 did not alter the maximum and fade responses to stimulation in 2 Hz paced atria. The blood flow into an isolated atrium was not changed detectably during stimulation. These results suggest that the fade of the inotropic response to parasympathetic nerve stimulation is related subsidiarily to acetylcholinesterase or washout of ACh at the neuroeffector junction in isolated perfused atria.

  3. Parent-Implemented Script Fading to Promote Play-Based Verbal Initiations in Children with Autism

    ERIC Educational Resources Information Center

    Reagon, Kara A.; Higbee, Thomas S.

    2009-01-01

    We trained 3 mothers of children with autism to create, implement, and systematically fade scripts to promote vocal initiations during play. All 3 children's scripted and unscripted initiations increased after the introduction and fading of scripts, and unscripted initiations were maintained at the 2-week follow-up. The results indicate that…

  4. The FADE mass-stat: a technique for inserting or deleting particles in molecular dynamics simulations.

    PubMed

    Borg, Matthew K; Lockerby, Duncan A; Reese, Jason M

    2014-02-21

    The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually "fades-in" (inserts) or "fades-out" (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C60 Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.

  5. The FADE mass-stat: A technique for inserting or deleting particles in molecular dynamics simulations

    SciTech Connect

    Borg, Matthew K.; Lockerby, Duncan A.; Reese, Jason M.

    2014-02-21

    The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually “fades-in” (inserts) or “fades-out” (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C{sub 60} Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.

  6. Stimulus Fading and Transfer in the Treatment of Self-Restraint and Self-Injurious Behavior.

    ERIC Educational Resources Information Center

    Pace, Gary M.; And Others

    1986-01-01

    Manipulation of mechanical restraint properties were conducted in separate studies with two profoundly retarded adolescents who exhibited both self-restraint and self-injurious behavior. Techniques included prompting, differential reinforcement, and stimulus fading. Results suggested that stimulus fading and transfer may be valuable components in…

  7. Using Video Prompting with Different Fading Procedures to Teach Daily Living Skills: A Preliminary Examination

    ERIC Educational Resources Information Center

    Wu, Pei-Fang; Cannella-Malone, Helen I.; Wheaton, Joe E.; Tullis, Chris A.

    2016-01-01

    Two students with developmental disabilities were taught two daily living skills using video prompting with error correction presented on an iPod Touch, and two different fading procedures were implemented. In one fading procedure, individual video clips were merged into multiple larger clips following acquisition of the entire skill. In the…

  8. Using Stimulus Fading without Escape Extinction to Increase Compliance with Toothbrushing in Children with Autism

    ERIC Educational Resources Information Center

    Bishop, Michele R.; Kenzer, Amy L.; Coffman, Christine M.; Tarbox, Courtney M.; Tarbox, Jonathan; Lanagan, Taira M.

    2013-01-01

    Routine toothbrushing is an essential part of good oral hygiene. This study investigated the use of stimulus fading without escape extinction to increase compliance with toothbrushing with three children with autism spectrum disorder (ASD). A 30-step stimulus fading hierarchy was implemented; gradually increasing the proximity of the toothbrush to…

  9. Stimulus Fading and Differential Reinforcement for the Treatment of Needle Phobia in a Youth with Autism

    ERIC Educational Resources Information Center

    Shabani, Daniel B.; Fisher, Wayne W.

    2006-01-01

    Stimulus fading in the form of gradually increased exposure to a fear-evoking stimulus, often combined with differential reinforcement, has been used to treat phobias in children who are otherwise normal and in children with autism. In this investigation, we applied stimulus fading plus differential reinforcement with an adolescent with autism and…

  10. Fading of artificial hair color and its prevention by photofilters.

    PubMed

    Locke, B; Jachowicz, J

    2005-01-01

    Fading of artificial hair color has been investigated by simulating actual usage conditions through exposure to artificial radiation in a weatherometer, with 0.35 mW/(m(2) nm) at 340 nm, for 16 to 48 hours, and by periodical washing. Hair color was produced by using commercial two-part, permanent hair dyes with light auburn, medium auburn, and dark auburn shades. Formulations based on red couplers, such as 4-amino-2-hydroxytoluene and 1-naphtol, as well as primary intermediates, such as 1-hydroxyethyl-4,5-diamino pyrazole sulfate, were employed. Results indicate that the extent of fading, as measured by the total color change parameter, dE, is greatest for colored hair subjected to both irradiation and shampooing, and significantly smaller for hair undergoing only irradiation or washing. Color loss has been also found to be dependent upon the hair type employed, with colored natural white and bleached hair undergoing much greater change than colored brown hair. It has been also shown that hair color based on pyrazole intermediates displayed the deepest fading as a result of shampooing (dE approximately 4-6 after ten shampooings) and irradiation/shampooing (dE approximately 14-16 after 32 hours of light exposure and four shampooings). The contribution of UV light (UVB + UVA) to the artificial hair-color loss was found experimentally to be dependent upon the irradiation dose and varied from 63% at 16 hours of irradiation time to 27% at 48 hours of light exposure. The theoretical extent of photoprotection by a formulation was assessed by calculating the percentage of UV light it attenuates in the wavelength range from 290 nm to 400 nm. The results indicate that UVB photofilters, such as octyl methoxy cinnamate, absorb less than 25% of the total UV irradiation at concentrations as high as 30 mg/(g hair). UVA absorbers were found to be more effective, with benzophenone-3 and benzophenone-4 absorbing about 40% of UV at the same concentration. Corresponding experimental

  11. Atropine and ODQ antagonize tetanic fade induced by L-arginine in cats.

    PubMed

    Cruciol-Souza, J M; Alves-Do-Prado, W

    1999-10-01

    Although it has been demonstrated that nitric oxide (NO) released from sodium nitrite induces tetanic fade in the cat neuromuscular preparations, the effect of L-arginine on tetanic fade and its origin induced by NO have not been studied in these preparations. Furthermore, atropine reduces tetanic fade induced by several cholinergic and anticholinergic drugs in these preparations, whose mechanism is suggested to be mediated by the interaction of acetylcholine with inhibitory presynaptic muscarinic receptors. The present study was conducted in cats to determine the effects of L-arginine alone or after pretreatment with atropine or 1H-[1,2, 4]oxadiazole [4,3-a]quinoxalin-1-one (ODQ) on neuromuscular preparations indirectly stimulated at high frequency. Drugs were injected into the middle genicular artery. L-arginine (2 mg/kg) and S-nitroso-N-acetylpenicillamine (SNAP; 16 microg/kg) induced tetanic fade. The Nomega-nitro-L-arginine (L-NOARG; 2 mg/kg) alone did not produce any effect, but reduced the tetanic fade induced by L-arginine. D-arginine (2 mg/kg) did not induce changes in tetanic fade. The tetanic fade induced by L-arginine or SNAP was reduced by previous injection of atropine (1.0 microg/kg) or ODQ (15 microg/kg). ODQ alone did not change tetanic fade. The data suggest that the NO-synthase-GC pathway participates in the L-arginine-induced tetanic fade in cat neuromuscular preparations. The tetanic fade induced by L-arginine probably depends on the action of NO at the presynaptic level. NO may stimulate guanylate cyclase increasing acetylcholine release and thereby stimulating presynaptic muscarinic receptors.

  12. The rapid extreme fading of GX 339-4

    NASA Astrophysics Data System (ADS)

    Maccarone, Thomas J.; Russell, David M.; Glamorgan, Fraser Lewis

    2012-07-01

    We report on a rapid fading of GX 339-4 to its lowest ever observed X-ray flux level. In response to the recent report of the start of an outburst of GX 339-4 (ATel #4162), we submitted a Swift TOO to check its X-ray flux. The observations were performed on July 8, 2012, from 14:00:59 to 15:53:55 UT. The live on-source exposure time of the observations was 2193 seconds. To our surprise, the source was not significantly detected, with a count rate of 0.0025+-0.0017 cts/sec from 0.3-10 keV, using Phil Evans' standard pipeline (Evans et al.

  13. Peer-Monitoring vs. Micro-Script Fading for Enhancing Knowledge Acquisition when Learning in Computer-Supported Argumentation Environments

    ERIC Educational Resources Information Center

    Bouyias, Yannis; Demetriadis, Stavros

    2012-01-01

    Research on computer-supported collaborative learning (CSCL) has strongly emphasized the value of providing student support with micro-scripts, which should withdraw (fade-out) allowing students to practice the acquired skills. However, research on fading shows conflicting results and some researchers suggest that the impact of fading is enhanced…

  14. Optimal throughput for cognitive radio with energy harvesting in fading wireless channel.

    PubMed

    Vu-Van, Hiep; Koo, Insoo

    2014-01-01

    Energy resource management is a crucial problem of a device with a finite capacity battery. In this paper, cognitive radio is considered to be a device with an energy harvester that can harvest energy from a non-RF energy resource while performing other actions of cognitive radio. Harvested energy will be stored in a finite capacity battery. At the start of the time slot of cognitive radio, the radio needs to determine if it should remain silent or carry out spectrum sensing based on the idle probability of the primary user and the remaining energy in order to maximize the throughput of the cognitive radio system. In addition, optimal sensing energy and adaptive transmission power control are also investigated in this paper to effectively utilize the limited energy of cognitive radio. Finding an optimal approach is formulated as a partially observable Markov decision process. The simulation results show that the proposed optimal decision scheme outperforms the myopic scheme in which current throughput is only considered when making a decision.

  15. Optimal throughput for cognitive radio with energy harvesting in fading wireless channel.

    PubMed

    Vu-Van, Hiep; Koo, Insoo

    2014-01-01

    Energy resource management is a crucial problem of a device with a finite capacity battery. In this paper, cognitive radio is considered to be a device with an energy harvester that can harvest energy from a non-RF energy resource while performing other actions of cognitive radio. Harvested energy will be stored in a finite capacity battery. At the start of the time slot of cognitive radio, the radio needs to determine if it should remain silent or carry out spectrum sensing based on the idle probability of the primary user and the remaining energy in order to maximize the throughput of the cognitive radio system. In addition, optimal sensing energy and adaptive transmission power control are also investigated in this paper to effectively utilize the limited energy of cognitive radio. Finding an optimal approach is formulated as a partially observable Markov decision process. The simulation results show that the proposed optimal decision scheme outperforms the myopic scheme in which current throughput is only considered when making a decision. PMID:24574885

  16. Average BER of subcarrier intensity modulated free space optical systems over the exponentiated Weibull fading channels.

    PubMed

    Wang, Ping; Zhang, Lu; Guo, Lixin; Huang, Feng; Shang, Tao; Wang, Ranran; Yang, Yintang

    2014-08-25

    The average bit error rate (BER) for binary phase-shift keying (BPSK) modulation in free-space optical (FSO) links over turbulence atmosphere modeled by the exponentiated Weibull (EW) distribution is investigated in detail. The effects of aperture averaging on the average BERs for BPSK modulation under weak-to-strong turbulence conditions are studied. The average BERs of EW distribution are compared with Lognormal (LN) and Gamma-Gamma (GG) distributions in weak and strong turbulence atmosphere, respectively. The outage probability is also obtained for different turbulence strengths and receiver aperture sizes. The analytical results deduced by the generalized Gauss-Laguerre quadrature rule are verified by the Monte Carlo simulation. This work is helpful for the design of receivers for FSO communication systems.

  17. Methods and Apparatuses for Signaling with Geometric Constellations in a Raleigh Fading Channel

    NASA Technical Reports Server (NTRS)

    Barsoum, Maged F. (Inventor); Jones, Christopher R. (Inventor)

    2015-01-01

    Communication systems are described that use signal constellations, which have unequally spaced (i.e., `geometrically` shaped) points. In many embodiments, the communication systems use specific geometric constellations that are capacity optimized at a specific SNR (signal to noise ratio). In addition, ranges within which the constellation points of a capacity optimized constellation can be perturbed and are still likely to achieve a given percentage of the optimal capacity increase compared to a constellation that maximizes d (sub min) (i.e. minimum distance between constellations) are also described. Capacity measures that are used in the selection of the location of constellation points include, but are not limited to, parallel decode (PD) capacity and joint capacity.

  18. An implementation of a reference symbol approach to generic modulation in fading channels

    NASA Technical Reports Server (NTRS)

    Young, R. J.; Lodge, J. H.; Pacola, L. C.

    1990-01-01

    As mobile satellite communications systems evolve over the next decade, they will have to adapt to a changing tradeoff between bandwidth and power. This paper presents a flexible approach to digital modulation and coding that will accommodate both wideband and narrowband schemes. This architecture could be the basis for a family of modems, each satisfying a specific power and bandwidth constraint, yet all having a large number of common signal processing blocks. The implementation of this generic approach, with general purpose digital processors for transmission of 4.8 kilobits per sec. digitally encoded speech, is described.

  19. Modeling of twitch fade based on slow interaction of nondepolarizing muscle relaxants with the presynaptic receptors.

    PubMed

    Bhatt, Shashi B; Amann, Anton; Nigrovic, Vladimir

    2006-08-01

    Nondepolarizing muscle relaxants (MRs) diminish the indirectly evoked single twitch due to their binding to the postsynaptic receptors. Additionally, the MRs produce progressive diminution of successive twitches upon repetitive stimulation (fade). Our study addresses the generation of fade as observed under clinical situation. The study was conducted in two phases. In the clinical part, we have evaluated the time course of twitch depression and fade following the administration of several doses of three MRs (rocuronium, pancuronium, and cisatracurium). In the second part, we have modified our model of neuromuscular transmission to simulate the time course of twitch depression and fade. The MR was assumed to bind to a single site on the presynaptic receptor to produce fade. The rates of interaction with the presynaptic receptors were characterized in terms of the arbitrarily assigned equilibrium dissociation constant and the half-life for dissociation of the presynaptic complex. A method was developed to relate the release of acetylcholine to the occupancy of the presynaptic receptors. The strength of the first and the fourth twitch was calculated from the peak concentration of the activated postsynaptic receptors, i.e., of those receptors with both sites occupied by acetylcholine. Our results indicate that, while the affinity of the MR for the presynaptic receptor plays little role in the time course of fade, the rate of dissociation of the complex between the presynaptic receptors and the muscle relaxant may be critical in determining the time course of fade. Tentative estimates of this parameter are offered.

  20. Channel Characterization and Robust Tracking for Diversity Reception over Time-Variant Off-Body Wireless Communication Channels

    NASA Astrophysics Data System (ADS)

    Van Torre, Patrick; Vallozzi, Luigi; Rogier, Hendrik; Moeneclaey, Marc; Verhaevert, Jo

    2010-12-01

    In the 2.45 GHz band, indoor wireless off-body data communication by a moving person can be problematic due to time-variant signal fading and the consequent variation in channel parameters. Off-body communication specifically suffers from the combined effects of fading, shadowing, and path loss due to time-variant multipath propagation in combination with shadowing by the human body. Measurements are performed to analyze the autocorrelation, coherence time, and power spectral density for a person equipped with a wearable receive system moving at different speeds for different configurations and antenna positions. Diversity reception with multiple textile antennas integrated in the clothing provides a means of improving the reliability of the link. For the dynamic channel estimation, a scheme using hard decision feedback after MRC with adaptive low-pass filtering is demonstrated to be successful in providing robust data detection for long data bursts, in the presence of dramatic channel variation.

  1. Text-fading based training leads to transfer effects on children's sentence reading fluency.

    PubMed

    Nagler, Telse; Korinth, Sebastian P; Linkersdörfer, Janosch; Lonnemann, Jan; Rump, Björn; Hasselhorn, Marcus; Lindberg, Sven

    2015-01-01

    Previous studies used a text-fading procedure as a training tool with the goal to increase silent reading fluency (i.e., proficient reading rate and comprehension). In recently published studies, this procedure resulted in lasting reading enhancements for adult and adolescent research samples. However, studies working with children reported mixed results. While reading rate improvements were observable for Dutch reading children in a text-fading training study, reading fluency improvements in standardized reading tests post-training attributable to the fading manipulation were not detectable. These results raise the question of whether text-fading training is not effective for children or whether research design issues have concealed possible transfer effects. Hence, the present study sought to investigate possible transfer effects resulting from a text-fading based reading training program, using a modified research design. Over a period of 3 weeks, two groups of German third-graders read sentences either with an adaptive text-fading procedure or at their self-paced reading rate. A standardized test measuring reading fluency at the word, sentence, and text level was conducted pre- and post-training. Text level reading fluency improved for both groups equally. Post-training gains at the word level were found for the text-fading group, however, no significant interaction between groups was revealed for word reading fluency. Sentence level reading fluency gains were found for the text-fading group, which significantly differed from the group of children reading at their self-paced reading routine. These findings provide evidence for the efficacy of text-fading as a training method for sentence reading fluency improvement also for children. PMID:25713554

  2. The Maritime satellite communication channel - Channel model, performance of modulation and coding

    NASA Astrophysics Data System (ADS)

    Hagenauer, Joachim; Dolainsky, Frank; Lutz, Erich; Papke, Wolfgang; Schweikert, Robert

    1987-05-01

    Toward the year 2000, maritime satellite communications using the INMARSAT system will employ a second and third generation of satellites and new ship earth stations (SES). The new SES standards will use very small antennas with gains between 0 and 15 dBi. At the lower end of SES there will be no antenna stabilization. The communication channel for such small stations is described by a model including multipath fading, Doppler shift, and noise. The results of an extensive measurement program were used to determine the parameters of the channel model, which depend on antenna type and elevation angle. Analytical calculations as well as synthetic and stored channel hardware simulations have been sued to determine the performance of several modulation schemes. A complete data link using PSK modems with AFC/Costas loop, interleaving, and FEC codecs at 1.2 kbits/s, was built up around a hardware maritime channel simulator to study the performance of data transmission on the small SES maritime channel. Theoretical and measured results are given for interleaved Viterbi decoding with channel state information and Reed-Solomon codes. The measurements show that with interleaved FEC schemes, the required E(b)/N(o) for a BER of 0.00001 is in the range of 9-15 dB, and the effects of multipath fading are almost compensated for.

  3. Analysis of rain fade duration models for Earth-to-satellite path based on data measured in Malaysia

    NASA Astrophysics Data System (ADS)

    Dao, Hassan; Rafiqul, Islam Md; Al-Khateeb, Khalid A. S.

    2013-12-01

    Statistical analysis of rain fade duration is crucial information for system engineer to design and plan a fade mitigation technique (FMT) for the satellite communication system. An investigation is carried out based on data measured of one year period in Kuala Lumpur, Malaysia from satellite path of MEASAT3. This paper presents statistical analysis of measured fade duration on high elevation angle (77.4°) in Ku-band compared to three prediction models of fade duration. It is found that none of the models could predict measured fade duration distribution accurately.

  4. Simultaneous L-band and VHF ionospheric fading effects at the geomagnetic equator

    NASA Technical Reports Server (NTRS)

    Sessions, W. B.; Golden, T. S.

    1972-01-01

    Simultaneous observations of ionspheric fading of 1550 MHz and 136 MHz radio waves from the ATS-5 spacecraft were recorded on the geomagnetic equator at Ancon, Peru. The observations were made during a period around the 1971 spring equinox; they show fades as great as 27 db at 136 MHz, and 6 db at 1550 MHz. The general characteristics of the scintillation signatures at the two frequencies are discussed with emphasis on comparison of the two frequencies with respect to rates and depths of fades. Typical statistical distributions of signal levels are also presented from which time availabilities of the signals relative to the median levels can be derived.

  5. Evidence of trends in rain event size effecting trends in rain fade

    NASA Astrophysics Data System (ADS)

    Paulson, Kevin S.

    2016-03-01

    Rain gauge studies have shown that the incidence of rain at rates associated with outage on terrestrial links has shown an increasing trend in several countries over the last 30 years. However, no evidence is available from microwave links to show whether outage rates, or the incidence of fade, is similarly increasing. This paper presents evidence of fade trends, derived from a decade of rain radar data. Although a decade is too short a period to observe rain rate trends, evidence is presented that trends in the size of rain events is leading to changes in the relationship between point rain rates and rain fade. Furthermore, these trends are shown to vary significantly across the UK. Temporal trends in both rain rates and their link to rain fade, make it more difficult to adapt International Telecommunication Union Radiocommunication Reccomendations to a changing climate.

  6. Capacity fade in Sn-C nanopowder anodes due to fracture.

    PubMed

    Aifantis, Katerina E; Huang, Tao; Hackney, Stephen A; Sarakonsri, Thapanee; Yu, Aishui

    2012-01-01

    Sn based anodes allow for high initial capacities, which however cannot be retained due to the severe mechanical damage that occurs during Li-insertion and de-insertion. To better understand the fracture process during electrochemical cycling three different nanopowders comprised of Sn particles attached on artificial graphite, natural graphite or micro-carbon microbeads were examined. Although an initial capacity of 700 mAh g(-1) was obtained for all Sn-C nanopowders, a significant capacity fade took place with continuous electrochemical cycling. The microstructural changes in the electrodes corresponding to the changes in electrochemical behavior were studied by transmission and scanning electron microscopy. The fragmentation of Sn observed by microscopy correlates with the capacity fade, but this fragmentation and capacity fade can be controlled by controlling the initial microstructure. It was found that there is a dependence of the capacity fade on the Sn particle volume and surface area fraction of Sn on carbon.

  7. The Problem of Cometary Fading is Not a Problem

    NASA Astrophysics Data System (ADS)

    Weissman, Paul R.

    2011-04-01

    It has been recognized since Oort's classic paper in 1950 that the number of returning long-period comets, i.e., those with original inverse semi-major axes, 1/ao > 10-4 AU-1 (where ao is the semi-major axis of the comet's orbit before it entered the planetary system and referenced to the barycenter of the solar system) is less than would be predicted from the observed flux of dynamically new comets, i.e., those with 1/ao < 10-4 AU-1. To explain this, researchers have commonly assumed a "fading factor,” which is usually an exponential or power law decay in the removal probability or lifetime for returning comets. While mathematically convenient, these functions do not necessarily relate to real physical processes that we know occur in comets, and may lead to their physical demise. A Monte Carlo model of the evolution of long-period comets from the Oort cloud is presented that incorporates these processes, including random disruption, sublimation of all volatiles, non-volatile crust formation on nucleus surfaces, and planetary impacts. Using this model, it is shown that a reasonably good fit to the observed 1/ao distribution can be achieved for 1/ao values between 0 and 8 x 10-3 AU-1 (semi-major axes between 125 AU and infinity). Observational selection effects will also be discussed. This work was supported by the NASA Planetary Astronomy Program.

  8. Joint Channel Estimation and Signal Detection for the OFDM System Without Cyclic Prefix Over Doubly-Selective Channels

    NASA Astrophysics Data System (ADS)

    Song, Lijun; Lei, Xia; Jin, Maozhu; Lv, Zhihan

    2015-12-01

    In the high-speed railway wireless communication, a joint channel estimation and signal detection algorithm is proposed for the orthogonal frequency division multiplexing (OFDM) system without cyclic prefix in the doubly-selective fading channels. Our proposed method first combines the basis expansion model (BEM) and the inter symbol interference (ISI) cancellation to overcome the situation that exists with the fast time-varying channel and the normalized maximum multipath channel exceeding the length of the cyclic prefix (CP). At first, the channel estimation and signal detection can be approximated without considering the ISI. Then, the channel parameters and signal detection are updated through ISI cancellation and circular convolution reconstruction from the frequency domain. The simulations show the algorithm can improve the performance of channel estimation and signal detection.

  9. Spoon-to-cup fading as treatment for cup drinking in a child with intestinal failure.

    PubMed

    Groff, Rebecca A; Piazza, Cathleen C; Zeleny, Jason R; Dempsey, Jack R

    2011-01-01

    We treated a child with intestinal failure who consumed solids on a spoon but not liquids from a cup. We used spoon-to-cup fading, which consisted of taping a spoon to a cup and then gradually moving the bowl of the spoon closer to the edge of the cup. Spoon-to-cup fading was effective for increasing consumption of liquids from a cup. PMID:22219546

  10. SPOON-TO-CUP FADING AS TREATMENT FOR CUP DRINKING IN A CHILD WITH INTESTINAL FAILURE

    PubMed Central

    Groff, Rebecca A; Piazza, Cathleen C; Zeleny, Jason R; Dempsey, Jack R

    2011-01-01

    We treated a child with intestinal failure who consumed solids on a spoon but not liquids from a cup. We used spoon-to-cup fading, which consisted of taping a spoon to a cup and then gradually moving the bowl of the spoon closer to the edge of the cup. Spoon-to-cup fading was effective for increasing consumption of liquids from a cup. PMID:22219546

  11. Spoon-to-Cup Fading as Treatment for Cup Drinking in a Child with Intestinal Failure

    ERIC Educational Resources Information Center

    Groff, Rebecca A.; Piazza, Cathleen C.; Zeleny, Jason R.; Dempsey, Jack R.

    2011-01-01

    We treated a child with intestinal failure who consumed solids on a spoon but not liquids from a cup. We used spoon-to-cup fading, which consisted of taping a spoon to a cup and then gradually moving the bowl of the spoon closer to the edge of the cup. Spoon-to-cup fading was effective for increasing consumption of liquids from a cup. (Contains 2…

  12. Measurement and Modeling of Narrowband Channels for Ultrasonic Underwater Communications

    PubMed Central

    Cañete, Francisco J.; López-Fernández, Jesús; García-Corrales, Celia; Sánchez, Antonio; Robles, Encarnación; Rodrigo, Francisco J.; Paris, José F.

    2016-01-01

    Underwater acoustic sensor networks are a promising technology that allow real-time data collection in seas and oceans for a wide variety of applications. Smaller size and weight sensors can be achieved with working frequencies shifted from audio to the ultrasonic band. At these frequencies, the fading phenomena has a significant presence in the channel behavior, and the design of a reliable communication link between the network sensors will require a precise characterization of it. Fading in underwater channels has been previously measured and modeled in the audio band. However, there have been few attempts to study it at ultrasonic frequencies. In this paper, a campaign of measurements of ultrasonic underwater acoustic channels in Mediterranean shallow waters conducted by the authors is presented. These measurements are used to determine the parameters of the so-called κ-μ shadowed distribution, a fading model with a direct connection to the underlying physical mechanisms. The model is then used to evaluate the capacity of the measured channels with a closed-form expression. PMID:26907281

  13. Measurement and Modeling of Narrowband Channels for Ultrasonic Underwater Communications.

    PubMed

    Cañete, Francisco J; López-Fernández, Jesús; García-Corrales, Celia; Sánchez, Antonio; Robles, Encarnación; Rodrigo, Francisco J; Paris, José F

    2016-01-01

    Underwater acoustic sensor networks are a promising technology that allow real-time data collection in seas and oceans for a wide variety of applications. Smaller size and weight sensors can be achieved with working frequencies shifted from audio to the ultrasonic band. At these frequencies, the fading phenomena has a significant presence in the channel behavior, and the design of a reliable communication link between the network sensors will require a precise characterization of it. Fading in underwater channels has been previously measured and modeled in the audio band. However, there have been few attempts to study it at ultrasonic frequencies. In this paper, a campaign of measurements of ultrasonic underwater acoustic channels in Mediterranean shallow waters conducted by the authors is presented. These measurements are used to determine the parameters of the so-called κ-μ shadowed distribution, a fading model with a direct connection to the underlying physical mechanisms. The model is then used to evaluate the capacity of the measured channels with a closed-form expression. PMID:26907281

  14. Measurement and Modeling of Narrowband Channels for Ultrasonic Underwater Communications.

    PubMed

    Cañete, Francisco J; López-Fernández, Jesús; García-Corrales, Celia; Sánchez, Antonio; Robles, Encarnación; Rodrigo, Francisco J; Paris, José F

    2016-02-19

    Underwater acoustic sensor networks are a promising technology that allow real-time data collection in seas and oceans for a wide variety of applications. Smaller size and weight sensors can be achieved with working frequencies shifted from audio to the ultrasonic band. At these frequencies, the fading phenomena has a significant presence in the channel behavior, and the design of a reliable communication link between the network sensors will require a precise characterization of it. Fading in underwater channels has been previously measured and modeled in the audio band. However, there have been few attempts to study it at ultrasonic frequencies. In this paper, a campaign of measurements of ultrasonic underwater acoustic channels in Mediterranean shallow waters conducted by the authors is presented. These measurements are used to determine the parameters of the so-called κ-μ shadowed distribution, a fading model with a direct connection to the underlying physical mechanisms. The model is then used to evaluate the capacity of the measured channels with a closed-form expression.

  15. Dynamic propagation channel characterization and modeling for human body communication.

    PubMed

    Nie, Zedong; Ma, Jingjing; Li, Zhicheng; Chen, Hong; Wang, Lei

    2012-12-18

    This paper presents the first characterization and modeling of dynamic propagation channels for human body communication (HBC). In-situ experiments were performed using customized transceivers in an anechoic chamber. Three HBC propagation channels, i.e., from right leg to left leg, from right hand to left hand and from right hand to left leg, were investigated under thirty-three motion scenarios. Snapshots of data (2,800,000) were acquired from five volunteers. Various path gains caused by different locations and movements were quantified and the statistical distributions were estimated. In general, for a given reference threshold è = -10 dB, the maximum average level crossing rate of the HBC was approximately 1.99 Hz, the maximum average fade time was 59.4 ms, and the percentage of bad channel duration time was less than 4.16%. The HBC exhibited a fade depth of -4 dB at 90% complementary cumulative probability. The statistical parameters were observed to be centered for each propagation channel. Subsequently a Fritchman model was implemented to estimate the burst characteristics of the on-body fading. It was concluded that the HBC is motion-insensitive, which is sufficient for reliable communication link during motions, and therefore it has great potential for body sensor/area networks.

  16. Fade measurements at L-band and UHF in mountainous terrain for land mobile satellite systems

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius

    1988-01-01

    Fading results related to land mobile satellite communications at L-band (1502 MHz) and UHF (870 MHz) are described. These results were derived from an experiment performed in a series of canyon passes in the Boulder, Colorado region of the US. The experimental configuration involved a helicopter as the source platform, which maintained a relatively fixed geometry with a mobile van containing the receiver and data-acquisition system. An unobstructed line of sight between the radiating sources and the receiving van was, for the most part, also maintained. In this configuration, the dominant mechanism causing signal fading (or enhancement) is a result of multipath. The resulting fade distributions demonstrated that at the 1 percent and 5 percent levels, 5.5- and 2.6-dB fades were on the average exceeded at L-band and 4.8- and 2.4-dB at UHF, respectively, for a path elevation angle of 45 deg. The canyon results as compared with previous roadside-tree-shadowing results demonstrate that the deciding factor dictating fade margin for future land mobile satellite systems is tree shadowing rather than fades caused by multipath.

  17. Fade and tachyphylaxis of gastric acid secretory response to pentagastrin in rat isolated gastric mucosa.

    PubMed

    Hirst, B H; Holland, J; Parsons, M E; Price, C A

    1988-12-01

    1. Gastric acid secretory responses to pentagastrin were characterized in the rat isolated gastric mucosa. In particular, the mechanisms underlying fade, declining response upon continued stimulation, and tachyphylaxis, progressively reduced responses upon repeated stimulation, were investigated. 2. Pentagastrin, 10(-9)-10(-7) M, resulted in concentration-related increases in acid secretion, with a mean maximum of 2.65 mumol cm-2 h-1 in response to pentagastrin, 10(-7) M. Higher concentrations of pentagastrin produced sub-maximal secretory rates; we define this as auto-inhibition. The responses to all concentrations of pentagastrin demonstrated fade. The rate of fade was correlated with the maximum acid secretory rate, declining at about 36% of the peak over the first 16 min. 3. The PO2, PCO2, [HCO3-], pH, [glucose], [lactate], [Na+] and [K+] did not decline during the fade of the acid secretory response to pentagastrin, 10(-7) M. Addition of a second aliquot of pentagastrin was not able to reverse fade, but these tissues were responsive to histamine. Replacement of the serosal solution, before addition of a second aliquot of pentagastrin, increased the acid response from 3% to 24% of the first response. 4. Serosal solution from donor tissues, allowed to respond to pentagastrin and then the acid secretion to fade, was able to stimulate secretion in fresh recipient tissues, although at lower rates. 5. Acid secretory responses to a second dose of pentagastrin were not significantly different, whether the tissues were previously unstimulated, or stimulated with pentagastrin washed out after attaining its peak secretory response (after 10-20 min). The second response was significantly reduced if the first response was allowed to fade with the pentagastrin in contact for 100 min; i.e. fade significantly influenced the extent of tachyphylaxis. 6. Proglumide, 10(-2) M, a gastrin receptor antagonist, and omeprazole, 10(-5) M, an inhibitor of the gastric (H+ + K

  18. The fade of the response to acetylcholine at the rabbit isolated sino-atrial node.

    PubMed

    Boyett, M R; Roberts, A

    1987-12-01

    1. The effect of acetylcholine (ACh) on the frequency of spontaneous action potentials, recorded with glass microelectrodes from small preparations of the sino-atrial node of the rabbit, has been investigated. 2. On application of ACh there was a rapid increase in cycle length (the interval between successive action potentials) but then, despite the continued presence of the ACh, cycle length decreased once again; i.e. the response to ACh 'faded' in the presence of ACh. This fade of the chronotropic response to ACh has been characterized. 3. To observe fade it was found to be important to use a fast flow bath in order to increase the ACh concentration at the preparation abruptly. In other words, the response to ACh was sensitive to the rate of increase in the ACh concentration at the tissue. This may explain why in one study of the sino-atrial node of the guinea-pig the authors failed to observe fade. 4. The concentration dependence of fade was studied in two ways: either as the fade in the response with different doses of ACh, or as the decrease in the response to a fixed test dose applied after a variable conditioning dose. Both methods indicated that fade increased with concentration over the range of roughly 10(-7) to 10(-5) M-ACh. 5. The onset of fade, i.e. the decline in cycle length during an exposure to ACh, was monophasic with low doses of ACh and biphasic (with fast and slow phases) with higher doses. The mean half-times of the fast and slow phases of fade were 10 +/- 2 s and 240 +/- 30 s (mean +/- S.E.M.; n = 5). However, in some preparations, rather than a smooth decrease in cycle length, there were discontinuities and cycle length could decrease in a stepwise fashion or even transiently alternate between two distinct states. 6. Time was required for recovery from fade because a response to a test dose applied soon after a conditioning dose was depressed. Recovery was studied by applying test doses at different times after conditioning doses. Recovery

  19. The fade of the response to acetylcholine at the rabbit isolated sino-atrial node.

    PubMed Central

    Boyett, M R; Roberts, A

    1987-01-01

    1. The effect of acetylcholine (ACh) on the frequency of spontaneous action potentials, recorded with glass microelectrodes from small preparations of the sino-atrial node of the rabbit, has been investigated. 2. On application of ACh there was a rapid increase in cycle length (the interval between successive action potentials) but then, despite the continued presence of the ACh, cycle length decreased once again; i.e. the response to ACh 'faded' in the presence of ACh. This fade of the chronotropic response to ACh has been characterized. 3. To observe fade it was found to be important to use a fast flow bath in order to increase the ACh concentration at the preparation abruptly. In other words, the response to ACh was sensitive to the rate of increase in the ACh concentration at the tissue. This may explain why in one study of the sino-atrial node of the guinea-pig the authors failed to observe fade. 4. The concentration dependence of fade was studied in two ways: either as the fade in the response with different doses of ACh, or as the decrease in the response to a fixed test dose applied after a variable conditioning dose. Both methods indicated that fade increased with concentration over the range of roughly 10(-7) to 10(-5) M-ACh. 5. The onset of fade, i.e. the decline in cycle length during an exposure to ACh, was monophasic with low doses of ACh and biphasic (with fast and slow phases) with higher doses. The mean half-times of the fast and slow phases of fade were 10 +/- 2 s and 240 +/- 30 s (mean +/- S.E.M.; n = 5). However, in some preparations, rather than a smooth decrease in cycle length, there were discontinuities and cycle length could decrease in a stepwise fashion or even transiently alternate between two distinct states. 6. Time was required for recovery from fade because a response to a test dose applied soon after a conditioning dose was depressed. Recovery was studied by applying test doses at different times after conditioning doses. Recovery

  20. HST Imaging of Giant Ionized Clouds Around Fading AGN

    NASA Astrophysics Data System (ADS)

    Keel, William C.; Maksym, W. P.; Bennert, V.; Schawinski, K.; Lintott, C. J.; Chojnowski, D.

    2013-01-01

    We present HST images in [O III], Hα, and adjacent continuum bands, for 7 AGN surrounding by photoionized clouds extending 10-35 kpc from the nuclei, whose energy budgets suggest substantial fading over timescales 30,000-100,000 years. These targets were found as a result of the efforts of nearly 200 Galaxy Zoo volunteers in both targeted and serendipitous searches, aimed at finding objects similar to Hanny's Voorwerp near IC 2497. The images reveal a fascinating variety of emission-line structures. Sub-kpc loops near the nuclei are frequent. A larger 5-kpc ring of emission appears near one AGN, not obviously connected to the gas near the nucleus. In NGC 5972, two systems of gas and dust appear, in a pattern suggesting that they result from a merger; there is a gap in line emission around the nucleus which would fit with a rapid cutoff in ionizing luminosity. Some of these clouds have their emission concentrated in very narrow filaments kiloparsecs in length, which might suggest a role for extensive magnetic fields. As in Hanny's Voorwerp, we see little spatial correlation between ionization parameter and Hα surface brightness, indicating that there is substantial density structure on yet-unresolved scales. The two AGN with large double radio sources show extended line emission perpendicular to the radio axis, violating a common pattern, as if the AGN axis had recently and rapidly precessed by ~90 degrees. This, plus the common signs of recent interaction in the hosts, informs our speculations on what might drive a rapid switch in the mode of energy output from accretion into the black holes in these objects, from radiative to kinetic, including the possibility that a special epoch near the merger of a binary black hole might be involved. This work has been supported by NASA through STSCI grant GO-12525.01.

  1. Channel simulation to facilitate mobile-satellite communications research

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz

    1987-01-01

    The mobile-satellite-service channel simulator, which is a facility for an end-to-end hardware simulation of mobile satellite communications links is discussed. Propagation effects, Doppler, interference, band limiting, satellite nonlinearity, and thermal noise have been incorporated into the simulator. The propagation environment in which the simulator needs to operate and the architecture of the simulator are described. The simulator is composed of: a mobile/fixed transmitter, interference transmitters, a propagation path simulator, a spacecraft, and a fixed/mobile receiver. Data from application experiments conducted with the channel simulator are presented; the noise converison technique to evaluate interference effects, the error floor phenomenon of digital multipath fading links, and the fade margin associated with a noncoherent receiver are examined. Diagrams of the simulator are provided.

  2. Pilot-aided chip-interleaved DS-CDMA transmission over time-varying channels (Invited Paper)

    NASA Astrophysics Data System (ADS)

    Na, Yanxin; Saquib, Mohammad; Win, Moe Z.

    2005-05-01

    Time-varying multipath fading associated with the wireless link limit the capacity of a wireless system. To adapt to this adverse radio environment efficiently, we investigate the use of a pilot-aided fade-resistant transmission scheme for the uplink of a chip-interleaved code division multiple access (CDMA) system. We analyze the trade-off between the number of diversity branches and the channel estimation error. We derive the optimum ratio of pilot signal power to information signal power. Our numerical study indicates that depending on the transmitter power and channel condition, the proposed system is capable of outperforming the conventional CDMA system.

  3. Investigation of mechanism of fade of gastrin-stimulated gastric acid secretion in the cat.

    PubMed

    Hirst, B H

    1988-01-01

    1. In conscious cats prepared with gastric fistulae gastric acid secretion in response to pentagastrin was found to reach a maximum after 45 min of stimulation, and to fade thereafter. Over the period 45-150 min of stimulation the fade was 5.4-7.8% of the maximum response per 15 min. 2. Once the response to pentagastrin had declined, acid secretion could not be restored by doubling the dose of pentagastrin, although an equisecretory dose of histamine could restore it. 3. Low doses of histamine were additive to the pentagastrin acid secretory response; they tended to prolong the peak response, but did not alter the subsequent fade of acid secretion. The histamine H1-receptor antagonist mepyramine did not affect maximal acid secretion or the fade of the pentagastrin response. 4. The beta-adrenoreceptor antagonist propranolol increased the secretory response to pentagastrin, whilst the alpha-adrenoreceptor antagonist phentolamine was without effect. Neither agent altered the fade of the pentagastrin response. Isoprenaline tended to inhibit pentagastrin-stimulated acid secretion and increase the rate of fade of the response. 5. The 5-hydroxytryptamine (5-HT) receptor antagonist methylsergide slightly enhanced the acid secretory response to pentagastrin, but did not alter the fade of the response. A low dose of 5-HT did not alter pentagastrin-stimulated acid secretion, whilst a higher dose of 5-HT inhibited it. 6. Tetra-, penta- and pentadecagastrin demonstrated tachyphylaxis, i.e. progressively reduced responses upon repeated stimulation, whilst histamine did not. A low dose of histamine did not prevent tachyphylaxis of the pentagastrin response. 7. It is concluded that fade of pentagastrin-stimulated acid secretion in the conscious cat cannot be satisfactorily explained by the failure of the acid secretory mechanism, depletion of histamine, release of 5-HT, or activation of histamine H1-, alpha- or beta-adreno-, or 5-HT-receptors. The similar characteristics of fade

  4. Correlation of capacity fading processes and electrochemical impedance spectra in lithium/sulfur cells

    NASA Astrophysics Data System (ADS)

    Risse, Sebastian; Cañas, Natalia A.; Wagner, Norbert; Härk, Eneli; Ballauff, Matthias; Friedrich, K. Andreas

    2016-08-01

    The capacity fading of lithium/sulfur (Li/S) cells is one major challenge that has to be overcome for a successful commercialization of this electrochemical storage system. Therefore it is essential to detect the major fading mechanisms for further improvements of this system. In this work, the processes leading to fading are analyzed in terms of a linear four state model and correlated to the distribution of relaxation times calculated with a modified Levenberg-Marquardt algorithm. Additionally, the Warburg impedance and the solution resistance are also obtained by the same algorithm. The detailed analysis of intermediate states during the first cycle gives the distinction between relaxation processes at the sulfur cathode and at the lithium anode. The influence of the polysulfides on the impedance parameters was evaluated using symmetric cells; this yields a good correlation with the results obtained from the first discharge/charge experiment. A fast and a slow capacity fading process are observed for the charge and the discharge during 50 cycles. The fast fading process can be assigned to Faradaic reactions at the lithium anode.

  5. FadE: whole genome methylation analysis for multiple sequencing platforms.

    PubMed

    Souaiaia, Tade; Zhang, Zheng; Chen, Ting

    2013-01-01

    DNA methylation plays a central role in genomic regulation and disease. Sodium bisulfite treatment (SBT) causes unmethylated cytosines to be sequenced as thymine, which allows methylation levels to reflected in the number of 'C'-'C' alignments covering reference cytosines. Di-base color reads produced by lifetech's SOLiD sequencer provide unreliable results when translated to bases because single sequencing errors effect the downstream sequence. We describe FadE, an algorithm to accurately determine genome-wide methylation rates directly in color or nucleotide space. FadE uses SBT unmethylated and untreated data to determine background error rates and incorporate them into a model which uses Newton-Raphson optimization to estimate the methylation rate and provide a credible interval describing its distribution at every reference cytosine. We sequenced two slides of human fibroblast cell-line bisulfite-converted fragment library with the SOLiD sequencer to investigate genome-wide methylation levels. FadE reported widespread differences in methylation levels across CpG islands and a large number of differentially methylated regions adjacent to genes which compares favorably to the results of an investigation on the same cell-line using nucleotide-space reads at higher coverage levels, suggesting that FadE is an accurate method to estimate genome-wide methylation with color or nucleotide reads. http://code.google.com/p/fade/.

  6. Explore the Effects of Microstructural Defects on Voltage Fade of Li- and Mn-Rich Cathodes

    DOE PAGES

    Hu, E.; Lyu, Y.; Xin, H.; Xin, H. L.; Liu, J.; Han, L.; Bak, S. -M.; Bai, J.; Yu, X.; Li, H.; et al

    2016-09-26

    Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layer to spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of x-ray diffraction (XRD), pair distribution function (PDF), x-ray absorption (XAS) techniques and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compoundmore » Li2Ru0.5Mn0.5O3. It is found that the nano-sized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nano-sized grain boundaries) and oxygen release form a positive feedback loop, promote each other during cycling, and accelerate the two major voltage fade contributors: the transition metal reduction and layered-to-spinel phase transition. These results clearly demonstrate the important relationships among the oxygen loss, microstructural defects and voltage fade. The importance of maintaining good crystallinity and protecting the surface of LMR material are also suggested.« less

  7. A pancultural perspective on the fading affect bias in autobiographical memory.

    PubMed

    Ritchie, Timothy D; Batteson, Tamzin J; Bohn, Annette; Crawford, Matthew T; Ferguson, Georgie V; Schrauf, Robert W; Vogl, Rodney J; Walker, W Richard

    2015-01-01

    The fading affect bias (FAB) refers to the negative affect associated with autobiographical events fading faster than the positive affect associated with such events, a reliable and valid valence effect established by researchers in the USA. The present study examined the idea that the FAB is a ubiquitous emotion regulating phenomenon in autobiographical memory that is present in people from a variety of cultures. We tested for evidence of the FAB by sampling more than 2400 autobiographical event descriptions from 562 participants in 10 cultures around the world. Using variations on a common method, each sample evidenced a FAB: positive affect faded slower than negative affect did. Results suggest that in tandem with local norms and customs, the FAB may foster recovery from negative life events and promote the retention of the positive emotions, within and outside of the USA. We discuss these findings in the context of Keltner and Haidt's levels of analysis theory of emotion and culture.

  8. Stimulus fading and transfer in the treatment of self-restraint and self-injurious behavior.

    PubMed Central

    Pace, G M; Iwata, B A; Edwards, G L; McCosh, K C

    1986-01-01

    We conducted several manipulations of mechanical restraint properties during the course of treatment for two profoundly retarded adolescents who exhibited both self-restraint and self-injurious behavior. In study 1, a combination of prompting, differential reinforcement, and stimulus fading reduced one subject's self-restraint, which consisted of holding rigid tubes on his arms. Subsequently, stimulus control of both self-restraint and self-injurious behavior was transferred to tennis wrist bands. In study 2, a second subject's self-restraint--placing his hands in his pants--was immediately eliminated by the use of air splints. Additionally, differential reinforcement and air-pressure fading resulted in the complete mobility of his arms and a substantial increase in appropriate behaviors. Results of this investigation suggest that stimulus fading and transfer may be valuable components in the elimination of self-restraint. PMID:3804871

  9. Stimulus Fading and Response Elaboration in Differential Reinforcement for Alternative Behavior

    PubMed Central

    Schlichenmeyer, Kevin J.; Dube, William V.; Vargas-Irwin, Mariela

    2015-01-01

    A hallmark of applied behavior analysis is the development of function-based interventions for problem behavior. A widely recommended function-based intervention is differential reinforcement of alternative behavior (DRA), in which reinforcement is contingent upon socially acceptable alternatives to problem behavior (e.g., teaching communication skills). Typically, DRA is introduced under rich schedules of reinforcement. Although effective for initiating behavior change, rich schedules are often impractical in the natural setting. In this study, we evaluated the extent to which a stimulus fading program could be employed to elaborate alternative behavior (mands) in two individuals diagnosed with an Autism Spectrum Disorder. For both participants, problem behavior was reduced substantially upon implementation of the DRA procedure. Further, problem behavior rates remained low and mand rates decreased to more practical levels as the DRA behavioral requirements increased during the fading program. The fading approach demonstrated in this paper may be a useful component of intervention packages for clinicians. PMID:25844032

  10. Joint Parameter Estimation for the Two-Wave with Diffuse Power Fading Model.

    PubMed

    Lopez-Fernandez, Jesus; Moreno-Pozas, Laureano; Lopez-Martinez, Francisco Javier; Martos-Naya, Eduardo

    2016-06-30

    Wireless sensor networks deployed within metallic cavities are known to suffer from a very severe fading, even in strong line-of-sight propagation conditions. This behavior is well-captured by the Two-Wave with Diffuse Power (TWDP) fading distribution, which shows great fit to field measurements in such scenarios. In this paper, we address the joint estimation of the parameters K and Δ that characterize the TWDP fading model, based on the observation of the received signal envelope. We use a moment-based approach to derive closed-form expressions for the estimators of K and Δ, as well as closed-form expressions for their asymptotic variance. Results show that the estimation error is close to the Cramer-Rao lower bound for a wide range of values of the parameters K and Δ. The performance degradation due to a finite number of observations is also analyzed.

  11. Systems implications of L-band fade data statistics for LEO mobile systems

    NASA Technical Reports Server (NTRS)

    Devieux, Carrie L.

    1993-01-01

    This paper examines and analyzes research data on the role of foliage attenuation in signal fading between a satellite transmitter and a terrestrial vehicle-mounted receiver. The frequency band of measurement, called L-Band, includes the region 1610.0 to 1626.5 MHz. Data from tests involving various combinations of foliage and vehicle movement conditions clearly show evidence of fast fading (in excess of 0.5 dB per millisecond) and fade depths as great or greater than 16 dB. As a result, the design of a communications link power control that provides the level of accuracy necessary for power sensitive systems could be significantly impacted. Specific examples of this include the communications links that employ Code Division Multiple Access (CDMA) as a modulation technique.

  12. Joint Parameter Estimation for the Two-Wave with Diffuse Power Fading Model

    PubMed Central

    Lopez-Fernandez, Jesus; Moreno-Pozas, Laureano; Lopez-Martinez, Francisco Javier; Martos-Naya, Eduardo

    2016-01-01

    Wireless sensor networks deployed within metallic cavities are known to suffer from a very severe fading, even in strong line-of-sight propagation conditions. This behavior is well-captured by the Two-Wave with Diffuse Power (TWDP) fading distribution, which shows great fit to field measurements in such scenarios. In this paper, we address the joint estimation of the parameters K and Δ that characterize the TWDP fading model, based on the observation of the received signal envelope. We use a moment-based approach to derive closed-form expressions for the estimators of K and Δ, as well as closed-form expressions for their asymptotic variance. Results show that the estimation error is close to the Cramer-Rao lower bound for a wide range of values of the parameters K and Δ. The performance degradation due to a finite number of observations is also analyzed. PMID:27376293

  13. Atmospheric-Fade-Tolerant Tracking and Pointing in Wireless Optical Communication

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo; Lee, Shinhak

    2003-01-01

    An acquisition, tracking, and pointing (ATP) system, under development at the time of reporting the information for this article, is intended to enable a terminal in a free-space optical communication system to continue to aim its transmitting laser beam toward a receiver at a remote terminal when the laser beacon signal from the remote terminal temporarily fades or drops out of sight altogether. Such fades and dropouts can be caused by adverse atmospheric conditions (e.g., rain or clouds). They can also occur when intervening objects block the line of sight between terminals as a result of motions of those objects or of either or both terminals

  14. Backwards Faded Scaffolding Impact on Pre-Service Teachers’ Cognition

    NASA Astrophysics Data System (ADS)

    Slater, T. F.; Slater, S. J.

    2009-12-01

    In response to national reform movements calling for future teachers to be prepared to design and deliver science instruction using the principles of inquiry in the context of Earth system science, we created and evaluated an innovative curriculum for specially designed courses for pre-service elementary education and secondary undergraduates based upon an inquiry-oriented teaching approach framed by the notions of backwards faded-scaffolding as an overarching theme for inquiry-oriented instruction. Students completed both structured- and open-inquiry projects using online scientific data bases, particularly those available from NASA, and presented the results of their investigations several times throughout the semester as a mini-science conference. Using a single-group, multiple-measures, quasi-experimental design, students demonstrated enhanced content knowledge of astronomy and inquiry as well as attitudes and self-efficacy toward teaching as measured by the Test of Astronomy STandards (TOAST), the Science Teaching Efficacy Belief Instrument - Version B, and the Attitudes Toward Science Inventory. We adopted a model of inquiry where: (i) students are engaged in questions; (ii) students are designing plans to pursue data; and (iii) students are generating and defending conclusions based on evidence they have collected. We developed an approach that is directly in contrast with the open inquiry “science fair” model to specifically use carefully scaffolded, shorter term inquiries, placing the most challenging aspects of “question generation” at the end of the lessons. In this model, during students' first experience with inquiry they are guided through the entire process, from research question to the appropriate content and format for a scientific conclusion. In their second experience, students generate their conclusions independently, with the previous experience set out as a guide for content and format. They are required to make sense of data that has

  15. Using Audio Script Fading and Multiple-Exemplar Training to Increase Vocal Interactions in Children with Autism

    ERIC Educational Resources Information Center

    Garcia-Albea, Elena; Reeve, Sharon A.; Brothers, Kevin J.; Reeve, Kenneth F.

    2014-01-01

    Script-fading procedures have been shown to be effective for teaching children with autism to initiate and participate in social interactions without vocal prompts from adults. In previous script and script-fading research, however, there has been no demonstration of a generalized repertoire of vocal interactions under the control of naturally…

  16. An Investigation of the Impact of Instructional Fading Using Completion Problems on Student Performance in Principles of Accounting Instruction

    ERIC Educational Resources Information Center

    Kingry, Mary Ann

    2012-01-01

    The effects of instructional fading using completion problems on student performance were investigated in this study. Instructional fading is the gradual withdrawal of the amount of assistance provided to the student and was accomplished in this study using completion problems. They were used to gradually transition the student from completely…

  17. Adaptive Pre-FFT Equalizer with High-Precision Channel Estimator for ISI Channels

    NASA Astrophysics Data System (ADS)

    Yoshida, Makoto

    We present an attractive approach for OFDM transmission using an adaptive pre-FFT equalizer, which can select ICI reduction mode according to channel condition, and a degenerated-inverse-matrix-based channel estimator (DIME), which uses a cyclic sinc-function matrix uniquely determined by transmitted subcarriers. In addition to simulation results, the proposed system with an adaptive pre-FFT equalizer and DIME has been laboratory tested by using a software defined radio (SDR)-based test bed. The simulation and experimental results demonstrated that the system at a rate of more than 100Mbps can provide a bit error rate of less than 10-3 for a fast multi-path fading channel that has a moving velocity of more than 200km/h with a delay spread of 1.9µs (a maximum delay path of 7.3µs) in the 5-GHz band.

  18. Characterisation of the LMS propagation channel at L- and S-bands: Narrowband experimental data and channel modelling

    NASA Technical Reports Server (NTRS)

    Sforza, Mario; Buonomo, Sergio

    1993-01-01

    During the period 1983-1992 the European Space Agency (ESA) carried out several experimental campaigns to investigate the propagation impairments of the Land Mobile Satellite (LMS) communication channel. A substantial amount of data covering quite a large range of elevation angles, environments, and frequencies was obtained. Results from the data analyses are currently used for system planning and design applications within the framework of the future ESA LMS projects. This comprehensive experimental data base is presently utilized also for channel modeling purposes and preliminary results are given. Cumulative Distribution Functions (PDF) and Duration of Fades (DoF) statistics at different elevation angles and environments were also included.

  19. Presynaptic facilitatory adenosine A2A receptors mediate fade induced by neuromuscular relaxants that exhibit anticholinesterase activity.

    PubMed

    Bornia, Elaine Cs; Correia-de-Sá, Paulo; Alves-Do-Prado, Wilson

    2011-03-01

    1. Pancuronium, cisatracurium and vecuronium are antinicotinic agents that, in contrast with d-tubocurarine and hexamethonium, exhibit anticholinesterase activity. Pancuronium-, cisatracurium- and vecuronium-induced fade results from blockade of facilitatory nicotinic receptors on motor nerves, but fade produced by such agents also depends on the presynaptic activation of inhibitory muscarinic M2 receptors by acetylcholine released from motor nerve terminals and activation of inhibitory adenosine A1 receptors by adenosine released from motor nerves and muscles. The participation of presynaptic facilitatory A2A receptors in fade caused by pancuronium, cisatracurium and vecuronium has not yet been investigated. In the present study, we determined the effects of ZM241385, an antagonist of presynaptic facilitatory A2A receptors, on fade produced by these neuromuscular relaxants in the rat phrenic nerve-diaphragm (PND) preparation. 2. The muscles were stimulated indirectly at 75±3Hz to induce a sustained tetanizing muscular contraction. The lowest concentration at which each antinicotinic agent produced fade without modifying initial tetanic tension (presynaptic action) was determined. 3. d-Tubocurarine-induced fade occurred only at 55 nmol/L, a concentration that also reduced maximal tetanic tension (post-synaptic action). At 10 nmol/L, ZM 241385 alone did not produce fade, but it did attenuate pancuronium (0.32 μmol/L)-, cisatracurium (0.32 μmol/L)- and vecuronium (0.36 μmol/L)-induced fade. 4. The fade induced by the 'pure' antinicotinic agents d-tubocurarine (55 nmol/L) and hexamethonium (413 μmol/L) was not altered by 10 nmol/L ZM 241385, indicating that presynaptic adenosine A2A receptors play a significant role in the fade produced by antinicotinic agents when such agents have anticholinesterase activity.

  20. Coverage area and fading time of surfactant-amended herbicidal droplets on cucurbitaceous leaves

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Proper use of appropriate surfactants to control droplet behaviors on leaf surfaces is critical to improve herbicide application efficacy for controlling paddy melons. An esterified seed oil surfactant and a petroleum oil surfactant were investigated to modify spread areas and fading times of water ...

  1. A Bayesian approach for Li-Ion battery capacity fade modeling and cycles to failure prognostics

    NASA Astrophysics Data System (ADS)

    Guo, Jian; Li, Zhaojun; Pecht, Michael

    2015-05-01

    Battery capacity fade occurs when battery capacity, measured in Ampere-hours, degrades over the number of charge/discharge cycles. This is a comprehensive result of various factors, including irreversible electrochemical reactions that form a solid electrolyte interphase (SEI) in the negative electrode and oxidative reactions of the positive electrode. The degradation mechanism is further complicated by operational and environmental factors such as discharge rate, usage and storage temperature, as well as cell-level and battery pack-level variations carried over from the manufacturing processes. This research investigates a novel Bayesian method to model battery capacity fade over repetitive cycles by considering both within-battery and between-battery variations. Physics-based covariates are integrated with functional forms for modeling the capacity fade. A systematic approach based on covariate identification, model selection, and a strategy for prognostics data selection is presented. The proposed Bayesian method is capable of quantifying the uncertainties in predicting battery capacity/power fade and end-of-life cycles to failure distribution under various operating conditions.

  2. Do the compact radio sources in NGC 253 and M82 fade over time?

    NASA Technical Reports Server (NTRS)

    Ulvestad, James S.; Antonucci, Robert R. J.

    1994-01-01

    The nearby starburst galaxy NGC 253 has been observed at a third epoch at 6 cm, and a second epoch at 3.6 cm, using the highest resolution configuration of the Very Large Array (VLA). Over a total time span of 4 yr between 1987 and 1991, no new compact radio sources have appeared. The flux density limit ranges from 3 mJy (3 times the power of Cas A) for most of the main body of the source to approximately 0.3 mJy off the diffuse source surrounding the nucleus. Furthermore, there is no evidence for significant source fading over 4 yr, in contrast to the result reported by Kronberg & Sramek (1985) for M82. More recent data suggest that, except for the strongest source in that galaxy, the compact radio sources in M82 may not be fading after all. If this suggestion proves correct, supernova rates of 0.2-0.3/yr in M82, estimated based on the assumed source fading, are incorrect. More accurate limits on source fading indicate that the current rate of production of radio supernovae in M82 is no greater than 0.1/yr, while that in NGC 253 is no greater than 0.25/yr.

  3. Script Fading to Promote Unscripted Bids for Joint Attention in Children with Autism

    ERIC Educational Resources Information Center

    Pollard, Joy S.; Betz, Alison M.; Higbee, Thomas S.

    2012-01-01

    We used a script-fading procedure to teach 3 children with autism to initiate bids for joint attention. We examined the effects of (a) scripts, (b) varied adult scripted responses, and (c) multiple-exemplar script training on promoting unscripted language during bids for joint attention. All 3 participants learned to initiate bids for joint…

  4. Fading test using the SAAD-POSL method for retrospective accidental dosimetry of building materials

    NASA Astrophysics Data System (ADS)

    Kim, M. J.; Lee, Y. J.; Lee, J. I.; Kim, J. L.; Hong, D. G.

    2015-11-01

    Fading test using the single aliquot additive dose method with pulsed optically stimulated luminescence (SAAD-POSL method) was applied to core-disc samples extracted from heated red brick, tile, roof-tile, and toilet porcelain after X-ray and beta irradiation. From thermoluminescence measurements of each material, the optimal preheat condition of the SAAD-POSL method was first determined as 170 °C for 10 s. Fading characteristics of core-disc samples of heated red brick obtained using the SAAD-POSL method were similar to those of quartz grains (90-250 μm) obtained using the SAR-OSL method, regardless of the differences in the sample and radiation type. Fading evaluations of the core-disc samples of these building materials two weeks after irradiation showed that the equivalent dose (ED) decreased between 5% and 42%. The results indicate that the fading characteristics will be able to contribute to a more accurate estimation of the ED value using the SAAD-POSL method.

  5. Capacity fade modelling of lithium-ion battery under cyclic loading conditions

    NASA Astrophysics Data System (ADS)

    Ashwin, T. R.; Chung, Yongmann M.; Wang, Jihong

    2016-10-01

    A pseudo two-dimensional (P2D) electro-chemical lithium-ion battery model is presented in this paper to study the capacity fade under cyclic charge-discharge conditions. The Newman model [1,2] has been modified to include a continuous solvent reduction reaction responsible for the capacity fade and power fade. The temperature variation inside the cell is accurately predicted using a distributed thermal model coupled with the internal chemical heat generation. The model is further improved by linking the porosity variation with the electrolyte partial molar concentration, thereby proving a stronger coupling between the battery performance and the chemical properties of electrolyte. The solid electrolyte interface (SEI) layer growth is estimated for different cut-off voltages and charging current rates. The results show that the convective heat transfer coefficient as well as the porosity variation influences the SEI layer growth and the battery life significantly. The choice of an electrolyte decides the conductivity and partial molar concentration, which is found to have a strong influence on the capacity fade of the battery. The present battery model integrates all essential electro-chemical processes inside a lithium-ion battery under a strong implicit algorithm, proving a useful tool for computationally fast battery monitoring system.

  6. Behavioral momentum and stimulus fading in the acquisition and maintenance of child compliance in the home

    PubMed Central

    Ducharme, Joseph M.; Worling, David E.

    1994-01-01

    The provision of a series of requests to which compliance is highly likely (high-probability requests) immediately antecedent to low-probability requests has been used to establish behavioral momentum of compliance. We evaluated a fading procedure for maintaining high levels of compliance obtained with high-probability requests. Fading involved a systematic reduction in the number of high-probability requests and an increase in the latency between the high- and low-probability requests. High levels of compliance for both “do” and “don't” requests were maintained for 16 weeks in a 5-year-old boy with developmental disabilities after the high-probability request sequence was faded. Similar maintenance was obtained for “do” requests in a 15-year-old girl with developmental disabilities. For this subject, however, the high-probability request sequence was ineffective with “don't” requests. When “don't” requests were phrased as “do” requests, the high-probability request sequence produced high levels of compliance to the low-probability request. High levels of compliance to these “do” requests were maintained for 16 weeks after the high-probability request sequence was faded. PMID:16795842

  7. Script Fading for Children with Autism: Generalization of Social Initiation Skills from School to Home

    ERIC Educational Resources Information Center

    Wichnick, Alison Marie

    2013-01-01

    A critical component of teaching social skills to people with autism is the generalization of behavior change across a variety of untrained situations during which social skills are appropriate. The script-fading procedure is an effective technology for teaching social skills to people with autism, but few researchers have established cues in the…

  8. A short-time fading study of Al2O3:C

    NASA Astrophysics Data System (ADS)

    Nascimento, L. F.; Vanhavere, F.; Silva, E. H.; Deene, Y. De

    2015-01-01

    This paper studies the short-time fading from Al2O3:C by measuring optically stimulated luminescence (OSL) signals (Total OSL: TOSL, and Peak OSL: POSL) from droplets and Luxel™ pellets. The influence of various bleaching regimes (blue, green and white) and light power is compared. The fading effect is the decay of the OSL signal in the dark at room temperature. Al2O3:C detectors were submitted to various bleaching regimes, irradiated with a reference dose and read out after different time spans. Investigations were carried out using 2 mm size droplet detectors, made of thin Al2O3:C powder mixed with a photocured polymer. Tests were compared to Luxel™-type detectors (Landauer Inc.). Short-time post-irradiation fading is present in OSL results (TOSL and POSL) droplets for time spans up to 200 s. The effect of short-time fading can be lowered/removed when treating the detectors with high-power and/or long time bleaching regimes; this result was observed in both TOSL and POSL from droplets and Luxel™.

  9. Using Reinforcer Pairing and Fading to Increase the Milk Consumption of a Preschool Child

    ERIC Educational Resources Information Center

    Tiger, Jeffrey H.; Hanley, Gregory P.

    2006-01-01

    The present study replicates and extends previous research on the treatment of food selectivity by implementing pairing and fading procedures to increase a child's milk consumption during regularly scheduled preschool meals. The treatment involved mixing a small amount of chocolate syrup into a glass of milk and gradually eliminating the…

  10. Teaching children with autism to engage in conversational exchanges: script fading with embedded textual stimuli.

    PubMed Central

    Sarokoff, R A; Taylor, B A; Poulson, C L

    2001-01-01

    A multiple baseline across three sets of stimuli was used to assess the effects of a script-fading procedure using embedded text to teach 2 children with autism to engage in conversation statements about the stimuli. Both students stated all the scripted statements, and unscripted statements also increased. Generalization was assessed with novel peers and with untrained stimuli. PMID:11317993

  11. Social Interaction Skills for Children with Autism: A Script-Fading Procedure for Beginning Readers.

    ERIC Educational Resources Information Center

    Krantz, Patricia J.; McClannahan, Lynn E.

    1998-01-01

    A study investigated the effectiveness in increasing social exchanges of embedding textual cues in the photographic activity schedules of three boys (ages 4-5) with autism. After learning to use the scripts, verbal elaborations and unscripted interactions increased. After scripts were faded, interactions continued and generalized to other…

  12. The Influence of Small Class Size, Duration, Intensity, and Heterogeneity on Head Start Fade

    ERIC Educational Resources Information Center

    Huss, Christopher D.

    2010-01-01

    The researcher conducted a nonexperimental study to investigate and analyze the influence of reduced class sizes, intensity (all day and every day), duration (five years), and heterogeneity (random class assignment) on the Head Start Fade effect. The researcher employed retrospective data analysis using a longitudinal explanatory design on data…

  13. Investigating Human Impact in the Environment with Faded Scaffolded Inquiry Supported by Technologies

    ERIC Educational Resources Information Center

    Campbell, Todd; Longhurst, Max; Duffy, Aaron M.; Wolf, Paul G.; Nagy, Robin

    2012-01-01

    Teaching science as inquiry is advocated in all national science education documents and by leading science and science teaching organizations. In addition to teaching science as inquiry, we recognize that learning experiences need to connect to students' lives. This article details how we use a sequence of faded scaffolded inquiry supported by…

  14. Mitigating Voltage Fade in Cathode Materials by Improving the Atomic Level Uniformity of Elemental Distribution

    SciTech Connect

    Zheng, Jianming; Gu, Meng; Genc, Arda; Xiao, Jie; Xu, Pinghong; Chen, Xilin; Zhu, Zihua; Zhao, Wenbo; Pullan, Lee; Wang, Chong M.; Zhang, Jiguang

    2014-04-07

    Li-rich and Mn-rich (LMR) layered structured materials are very promising cathodes for high-energy lithium-ion batteries. However, their fundamental structure and voltage fading mechanisms are far from being well understood. Here we report the first evidence on the reduced voltage and energy fade of LMR cathode by improving the atomic level spatial distribution of the chemical species. LMR cathode (Li[Li0.2Ni0.2M0.6]O2) prepared by co-precipitation and sol-gel methods are dominated by R-3m phase and show significant Ni-segregation at the surface of the particles. They exhibit large voltage-fade and fast capacity degradation. In contrast, LMR cathode prepared by hydrothermal assisted method is dominated by C2/m phase and minimal Ni-segregation. It also demonstrates much smaller voltage-fade and excellent capacity retention. The fundamental correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials found in this work also guide the design of other functional materials with enhanced stabilities.

  15. An electronic apparatus to measure the retinal-neural fading phenomena.

    PubMed

    Albee, J L; Albee, P R; Young, F A

    1977-12-01

    Fading and regeneration of visual stimuli is a phenomenon which occurs under the condition of redundant visual stimulation in the human eye. By totally encompassing a subject's visual field with large sheets of colored cardboard, which provided an undifferentiated ground, it was found that the color spontaneously disappeared and reappeared. This evidence suggested that the cycle is a fundamental aspect of the visual process. The Retinal-Neural Fading Phenomena Device was developed using light-emitting diodes (LED) as the stimulus source. This allowed the quantitative measurement of the rate of fade and degree of satiation the eye undergoes under a redundant presentation equivalent to stabilized images. The rate and degree of satiation to redundant stimulation appears to correlate highly with a subject's reading efficiency. The data suggested that rapid and deep satiation was the favored outcome if one is to be free from reading or perceptual disorders. This leads to the speculation that rapid fade of afterimages of previously read symbols is required to prepare the visual system for new material. Conversely, the inability to suppress afterimages may be a physiological factor in the "dyslexic syndrome."

  16. Intensification and fading of auroral arcs in the dusk-midnight sector of the polar cap

    SciTech Connect

    Wu, Q.; Rosenberg, T.J. ); Berkey, F.T. ); Eather, R.H. )

    1991-05-01

    Observations of the aurora from South Pole station (magnetic latitude = {minus}74.2{degree}) have been used to study the intensification and fading of polar arcs observed near the dusk meridian. Most of the cases examined have the following features in common: (1) a preexisting auroral form intensifies for about 10 min; (2) this activation is followed by a pronounced decrease of luminosity; (3) the auroral fade terminates after 30-60 min with the onset of intense aurora which sweeps rapidly overhead. The availability of all-sky camera, auroral electrojet (AE) index and interplanetary magnetic field (IMF) data for some of the cases enables the following additional characterizations of these events. The preexisting form is a Sun- or oval-aligned arc (or part of a multiple arc system) which disappears following the activation; equatorward drift of the arc (or system) accompanies the luminosity change. There is some evidence to suggest that the arc is poleward of the auroral oval. The brief intensification and/or the onset of fading occurs during the growth phase or near the start of the expansive phase of a substorm; termination of the fade is near the maximum in AE and is probably indicative of the beginning of the recovery phase of the substorm. For all three cases for which IMF data were available the onset of fading occurred 20-30 min after B{sub z} turned southward. Sun-aligned arcs are a common feature of the polar cap during northward B{sub z} but disappear during the increasingly disturbed conditions that accompany southward B{sub z}. The present results suggest that brief intensifications of southern hemisphere polar cap arcs near dusk may be linked in part to the sunward orientation of the IMF which favors enhanced electron fluxes in the southern lobe of the magnetotail.

  17. Unexpected Voltage Fade in LMR-NMC Oxides Cycled below the “Activation” Plateau

    SciTech Connect

    Li, Yan; Bareno, Javier; Bettge, Martin; Abraham, Daniel P

    2015-01-01

    A common feature of lithium-excess layered oxides, nominally of composition xLi2MnO3•(1-x)LiMO2 (M = transition metal) is a high-voltage plateau (~4.5 V vs. Li/Li+) in their capacity-voltage profile during the first delithiation cycle. This plateau is believed to result from activation of the Li2MnO3 component, which makes additional lithium available for electrochemical cycling. However, oxides cycled beyond this activation plateau are known to display voltage fade which is a continuous reduction in their equilibrium potential. In this article we show that these oxides display gradual voltage fade even on electrochemical cycling in voltage ranges well below the activation plateau. The average fade is ~0.08 mV-cycle-1 for Li1.2Ni0.15Mn0.55Co0.1O2 vs. Li cells after 20 cycles in the 2–4.1 V range at 55°C; a ~54 mV voltage hysteresis, expressed as the difference in average cell voltage between charge and discharge cycles, is also observed. The voltage fade results from a gradual accumulation of local spinel environments in the crystal structure. Some of these spinel sites result from lithium deficiencies during oxide synthesis and are likely to be at the particle surfaces; other sites result from the migration of transition metal atoms in the partially-delithiated LiMO2 component into the lithium planes during electrochemical cycling. The observed rate of voltage fade depends on a combination of factors that includes the phase equilibrium between the layered and spinel components and the kinetics of transition metal migration.

  18. DAPI-fluorescent fading: a problem in microscopy or a way to measure nuclear DNA content?

    NASA Astrophysics Data System (ADS)

    Gallardo-Escárate, Cristian; Álvarez-Borrego, Josué; Kober, V.; del Río-Portilla, Miguel Á.

    2006-01-01

    In observation by confocal or conventional fluorescence microscopy, the retardation of the lost in fluorescence, from highest signal of fluorescence to lowest intensity are important factors in order to obtain accurate images. This problem is very common in fluorochromes for nuclear DNA and especially for DAPI stain. The fluorescence of DAPI is rapidly lost when it is exposure to excitation by ultra violet (UV) light, and especially under optimal condition of observation. Although the fading process could be retardate by using of mounting medium with antifading solutions, the photochemical process underlying the fluorescence decay has not yet been fully explained. In addiction, neither relationship has been tested between the fluorescence fading and nuclear DNA content. However, the capacity of the DNA to absorb UV light is knows. In order to test this relationship we measured by means of image analysis the fluorescence intensity in several nuclei types during a fading period. The analysis was performed by an algorithm specifically built in MATLAB software. The relationship between nuclear DNA content and DAPI-fluorescence fading was found equal to 99%. This study demonstrates the feasibility for estimates genome size by quantification of fluorescence fading. In this context, the present method allows to measure nuclear DNA content in several medical applications (cancer, HIV, organ transplants, etc). Nowadays, for measuring DNA content, flow cytometry is widely used; however, with the flow cytometry method it is not possible to select a specific group of cells, such as from a specific region of a tumor. Moreover, the using of image analysis allows automatizing diagnostics procedures.

  19. TRP Channels

    NASA Astrophysics Data System (ADS)

    Voets, Thomas; Owsianik, Grzegorz; Nilius, Bernd

    The TRP superfamily represents a highly diverse group of cation-permeable ion channels related to the product of the Drosophila trp (transient receptor potential) gene. The cloning and characterization of members of this cation channel family has experienced a remarkable growth during the last decade, uncovering a wealth of information concerning the role of TRP channels in a variety of cell types, tissues, and species. Initially, TRP channels were mainly considered as phospholipase C (PLC)-dependent and/or store-operated Ca2+-permeable cation channels. More recent research has highlighted the sensitivity of TRP channels to a broad array of chemical and physical stimuli, allowing them to function as dedicated biological sensors involved in processes ranging from vision to taste, tactile sensation, and hearing. Moreover, the tailored selectivity of certain TRP channels enables them to play key roles in the cellular uptake and/or transepithelial transport of Ca2+, Mg2+, and trace metal ions. In this chapter we give a brief overview of the TRP channel superfamily followed by a survey of current knowledge concerning their structure and activation mechanisms.

  20. Joint TAS and power allocation for DF relaying M2M cooperative system

    NASA Astrophysics Data System (ADS)

    Xu, Lingwei; Zhang, Hao; Gulliver, T. Aaron

    2016-09-01

    The outage probability (OP) performance of transmit antenna selection (TAS) in a decode-and-forward relaying mobile-to-mobile system with relay selection over N-Nakagami fading channels is investigated. Exact closed-form expressions for the OP of two TAS schemes are derived, and the optimal power allocation optimisation problem is formulated. The OP performance is evaluated via Monte Carlo simulation to verify the analysis. The results obtained show that the optimal TAS scheme has better performance than the suboptimal TAS scheme, but the performance gap between these techniques decreases as the number of source antennas increases.

  1. Real-time joint source-channel coding of multiple correlated substream progressive sources for multiple-antenna Rayleigh channels

    NASA Astrophysics Data System (ADS)

    Farshchian, Masoud; Pearlman, William A.

    2008-01-01

    Recently, several methods that divide the original bitstream of an image/video progressive wavelet based source coders into multiple correlated substreams have been proposed. The principle behind transmitting independent multiple substream is to generate multiple descriptions of the source such that the graceful degradation is achieved when transmitted over severe fading channels and lossy packet networks since some of the streams may be recovered. Noting that multiple substream can benefit from multiple independent channel paths, we naturally consider Multi-Input Multi-Output communication systems where we obtain multiple independent fading channels. Depending on several factors including: the number of antennas employed, the transmission energy, the Doppler shift (due to the motion between the transmitter antenna and receiver antennas), the total transmission rate and the distortion-rate (D-R) of the source-there exists an optimal number of balanced substreams and an optimal joint source-channel coding policy such that the expected distortion at the receiver is minimized. In this paper we derive an expected distortion function at the receiver based on all of these parameters and provide a fast real-time numerical technique to find the optimal or near optimal number of balanced substreams to be transmitted. This expected distortion is based on our derivation of the probabilistic loss patterns of a balanced multiple substream progressive source coder. The accuracy of the derived expected distortion estimator is confirmed by Monte-Carlo simulation employing Dent's modification of Jakes' model. By accurately estimating the optimal number of balanced substreams to be transmitted, a substantial gain in visual quality at low and intermediate signal-to-noise ratio (SNR) is obtained over severely fading channels. At high SNR, the single stream source coder's source efficiency makes it slightly better than the multiple substream source coder. Overall, using our analytic

  2. Protection of oxidative hair color fading from shampoo washing by hydrophobically modified cationic polymers.

    PubMed

    Zhou, Y; Foltis, L; Moore, D J; Rigoletto, R

    2009-01-01

    The fading of oxidative color in hair as a result of daily shampoo washing activities has become a common problem and a source of frequent complaints by consumers. The fading occurs primarily through hair dye solubility in water. One aspect of the current study investigates the physical and chemical factors that influence hair color fading during the washing process. This is accomplished by testing hair dye dissolution in water from dyed hair samples with variation of surfactant type, pH, and hair type. Furthermore, a new approach to preventing color fading is developed aiming to provide an effective barrier function for hair dye from dissolving into water. The preliminary investigation of a series of polymers with various functional groups indicates that polymers with hydrophobically modified and cationic functionalities are most effective in preventing hair dye dissolution in water. It is also evident that a synergistic effect of the polymer's hydrophobic moieties and cationic charges are important on hair color protection during shampoo washing processes. A primary example of a polymer within this category is a cationic terpolymer of vinylpyrrolidone, dimethylaminopropyl methacrylamide, and methacryloylaminopropyl lauryldimonium chloride (INCI: Polyquaternium-55). The color protection benefit of this polymer is evaluated using newly developed methodologies for evaluating hair color changes, such as hair color fading tests through multiple shampoo washes with mannequin heads and hair tresses, both derived from human hair, colorimetry, and quantitative digital image analysis. In addition, new infrared spectroscopic imaging techniques are used to detect the hair dye deposition behavior inside hair fibers both with and without the color protection treatment. Both visual and instrumental measurement results indicate that Polyquaternium-55 provides a high level of color protection when formulated in a hair color protection regimen with up to 50% color protection. This

  3. Protection of oxidative hair color fading from shampoo washing by hydrophobically modified cationic polymers.

    PubMed

    Zhou, Y; Foltis, L; Moore, D J; Rigoletto, R

    2009-01-01

    The fading of oxidative color in hair as a result of daily shampoo washing activities has become a common problem and a source of frequent complaints by consumers. The fading occurs primarily through hair dye solubility in water. One aspect of the current study investigates the physical and chemical factors that influence hair color fading during the washing process. This is accomplished by testing hair dye dissolution in water from dyed hair samples with variation of surfactant type, pH, and hair type. Furthermore, a new approach to preventing color fading is developed aiming to provide an effective barrier function for hair dye from dissolving into water. The preliminary investigation of a series of polymers with various functional groups indicates that polymers with hydrophobically modified and cationic functionalities are most effective in preventing hair dye dissolution in water. It is also evident that a synergistic effect of the polymer's hydrophobic moieties and cationic charges are important on hair color protection during shampoo washing processes. A primary example of a polymer within this category is a cationic terpolymer of vinylpyrrolidone, dimethylaminopropyl methacrylamide, and methacryloylaminopropyl lauryldimonium chloride (INCI: Polyquaternium-55). The color protection benefit of this polymer is evaluated using newly developed methodologies for evaluating hair color changes, such as hair color fading tests through multiple shampoo washes with mannequin heads and hair tresses, both derived from human hair, colorimetry, and quantitative digital image analysis. In addition, new infrared spectroscopic imaging techniques are used to detect the hair dye deposition behavior inside hair fibers both with and without the color protection treatment. Both visual and instrumental measurement results indicate that Polyquaternium-55 provides a high level of color protection when formulated in a hair color protection regimen with up to 50% color protection. This

  4. A frequency-domain channel model and emulator for aeronautical communications

    NASA Astrophysics Data System (ADS)

    Yang, Xiaopeng; Liang, Jun; Yao, Kun; Shi, Haoshan

    2005-11-01

    In this paper, we propose a frequency domain simulation structure for aeronautical wideband frequency-selective channel, which features ground-air and air-air wireless links. With appropriate channel parameters, the emulator can model the parking, taxi and en-route scenarios. The wideband frequency-selective channel consists of some parallel sub-channels in frequency domain, which are assumed to be independent to each other and have Rayleigh-distributed envelopes. The sub-channel models and emulators are based on a simple structure and characterized by flat fading. Through such decomposition approach, a frequency domain frequency-selective channel model can be achieved, which is suitable for an implementation of orthogonal frequency-division multiplexing (OFDM) or multi-carrier code-division multi-access (MC-CDMA) channel emulator on computer. Some appropriate emulator parameters have been proposed through channel sounding data collected for different scenarios. Particularly, in order to emulate the time-varying fading model well, the parameter sets are generated from time to time before the simulation with the same statistics.

  5. Experimental Validation of Stochastic Wireless Urban Channel Model: Estimation and Prediction

    SciTech Connect

    Kuruganti, Phani Teja; Ma, Xiao; Djouadi, Seddik M

    2012-01-01

    Stochastic differential equations (SDE) can be used to describe the time-varying nature of wireless channels. This paper validates a long-term fading channel model for estimation and prediction from solely using measured received signal strength measurements. Such channel models can be used for optimizing wireless networks deployed for industrial automation, public access, and communication. This paper uses two different sets of received signal measurement data to estimate an predict the signal strength based on past measurements. The realworld performance of the estimation and prediction algorithm is demonstrated.

  6. Free-space optical channel simulator for weak-turbulence conditions.

    PubMed

    Bykhovsky, Dima

    2015-11-01

    Free-space optical (FSO) communication may be severely influenced by the inevitable turbulence effect that results in channel gain fluctuations and fading. The objective of this paper is to provide a simple and effective simulator of the weak-turbulence FSO channel that emulates the influence of the temporal covariance effect. Specifically, the proposed model is based on lognormal distributed samples with a corresponding correlation time. The simulator is based on the solution of the first-order stochastic differential equation (SDE). The results of the provided SDE analysis reveal its efficacy for turbulent channel modeling.

  7. RBF multiuser detector with channel estimation capability in a synchronous MC-CDMA system.

    PubMed

    Ko, K; Choi, S; Kang, C; Hong, D

    2001-01-01

    The authors propose a multiuser detector with channel estimation capability using a radial basis function (RBF) network in a synchronous multicarrier-code division multiple access (MC-CDMA) system. The authors propose to connect an RBF network to the frequency domain to effectively utilize the frequency diversity. Simulations were performed over frequency-selective and multi-path fading channels. These simulations confirmed that the proposed receiver can be used both for the channel estimation and as a multi-user receiver, thus permitting an increase in the number of active users. PMID:18249987

  8. Power Scaling of Uplink Massive MIMO Systems With Arbitrary-Rank Channel Means

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Jin, Shi; Wong, Kai-Kit; Zhu, Hongbo; Matthaiou, Michail

    2014-10-01

    This paper investigates the uplink achievable rates of massive multiple-input multiple-output (MIMO) antenna systems in Ricean fading channels, using maximal-ratio combining (MRC) and zero-forcing (ZF) receivers, assuming perfect and imperfect channel state information (CSI). In contrast to previous relevant works, the fast fading MIMO channel matrix is assumed to have an arbitrary-rank deterministic component as well as a Rayleigh-distributed random component. We derive tractable expressions for the achievable uplink rate in the large-antenna limit, along with approximating results that hold for any finite number of antennas. Based on these analytical results, we obtain the scaling law that the users' transmit power should satisfy, while maintaining a desirable quality of service. In particular, it is found that regardless of the Ricean $K$-factor, in the case of perfect CSI, the approximations converge to the same constant value as the exact results, as the number of base station antennas, $M$, grows large, while the transmit power of each user can be scaled down proportionally to $1/M$. If CSI is estimated with uncertainty, the same result holds true but only when the Ricean $K$-factor is non-zero. Otherwise, if the channel experiences Rayleigh fading, we can only cut the transmit power of each user proportionally to $1/\\sqrt M$. In addition, we show that with an increasing Ricean $K$-factor, the uplink rates will converge to fixed values for both MRC and ZF receivers.

  9. Fade-resistant photochromic reactions in a self-healable polymer.

    PubMed

    Saito, Mitsunori; Nishimura, Tatsuya; Hamazaki, Takamasa

    2015-10-01

    Molecular diffusion in a polymer matrix was studied to prevent degradation of photochromic reactions during repeated coloration-decoloration processes. Photochromic diarylethene was dispersed in polydimethylsiloxane (cured polymer), since it promoted exchange of damaged and fresh molecules owing to high diffusivity. The diffusion coefficient was evaluated by measuring a distribution of dye molecules that were colored within a narrow laser beam path. Temporal change of the distribution fitted well to theoretical curves that were drawn according to the 2-D solutions of Fick's equation. The experimental results indicated a fifteen-fold enhancement of the diffusion coefficient (0.0015 mm(2)/s) when the polymer was swollen with toluene. Fading of this photochromic polymer was examined by repeating alternative irradiation of violet and green laser beams. Although a non-swollen polymer faded seriously within 1,000 photochromic cycles, a swollen polymer exhibited an excellent photochromic function even after 30,000 cycles.

  10. Social interaction skills for children with autism: a script-fading procedure for beginning readers.

    PubMed Central

    Krantz, P J; McClannahan, L E

    1998-01-01

    Engaging in spontaneous social exchanges is a central skill deficit of children with autism, and one that is often difficult to remediate. The 3 boys (ages 4, 4, and 5 years) who participated in this study had acquired small verbal repertoires, but typically spoke only when answering questions or requesting preferred edible items or toys, and did not converse with a familiar teacher during baseline. During teaching, textual cues ("Look" and "Watch me") were embedded in the youngsters' photographic activity schedules; after learning to use the scripts, the children's verbal elaborations and unscripted interactions increased and were maintained when a new recipient of interaction was introduced. After scripts were faded, unscripted interactions not only continued but also generalized to different activities that had not been the topic of teaching. The script-fading procedure enabled children with autism to converse with adults, to benefit from adults' language models, and to engage in language practice that contributes to fluency. PMID:9652099

  11. Herpes simplex virus-cell interactions studied by low-fading contrasted immunofluorescence.

    PubMed

    Jensen, Helle Lone; Norrild, Bodil

    2005-01-01

    The low-fading immunofluorescence with propidium iodide contrast described here is recommended for light and confocal viral antigen identification and other cell biology studies because: (1) it is a simple, rapid, sensitive, and reproducible technique; (2) phase-contrast microscopy is unnecessary; (3) contrast is optimal without blurring the fluorescent labeling; (4) autofluorescence is minimal, even in fixed cells; (5) background staining is minimal; (6) fading is invisible for at least 5-min exposures, even in preparations with weak antigen presentation; (7) fluorescence is stable after storage in the dark at -20 degrees C; (8) fluorochromes are small-sized markers without steric hindrance; and (9) there is no need for silver enhancement or substrate solutions, which increase the risk of diffusion and other artifacts.

  12. Social interaction skills for children with autism: a script-fading procedure for beginning readers.

    PubMed

    Krantz, P J; McClannahan, L E

    1998-01-01

    Engaging in spontaneous social exchanges is a central skill deficit of children with autism, and one that is often difficult to remediate. The 3 boys (ages 4, 4, and 5 years) who participated in this study had acquired small verbal repertoires, but typically spoke only when answering questions or requesting preferred edible items or toys, and did not converse with a familiar teacher during baseline. During teaching, textual cues ("Look" and "Watch me") were embedded in the youngsters' photographic activity schedules; after learning to use the scripts, the children's verbal elaborations and unscripted interactions increased and were maintained when a new recipient of interaction was introduced. After scripts were faded, unscripted interactions not only continued but also generalized to different activities that had not been the topic of teaching. The script-fading procedure enabled children with autism to converse with adults, to benefit from adults' language models, and to engage in language practice that contributes to fluency.

  13. Systems, methods and computer-readable media for modeling cell performance fade of rechargeable electrochemical devices

    DOEpatents

    Gering, Kevin L

    2013-08-27

    A system includes an electrochemical cell, monitoring hardware, and a computing system. The monitoring hardware periodically samples performance characteristics of the electrochemical cell. The computing system determines cell information from the performance characteristics of the electrochemical cell. The computing system also develops a mechanistic level model of the electrochemical cell to determine performance fade characteristics of the electrochemical cell and analyzing the mechanistic level model to estimate performance fade characteristics over aging of a similar electrochemical cell. The mechanistic level model uses first constant-current pulses applied to the electrochemical cell at a first aging period and at three or more current values bracketing a first exchange current density. The mechanistic level model also is based on second constant-current pulses applied to the electrochemical cell at a second aging period and at three or more current values bracketing the second exchange current density.

  14. Atmospheric parameter estimation from AO wavefront sensing data: application of the FADE method with NACO

    NASA Astrophysics Data System (ADS)

    Brunner, Elisabeth; Girard, Julien H.

    2014-08-01

    The performance of a ground based telescope can depend greatly on the coherence time, a site and time varying parameter determining the required reaction bandwidth of an Adaptive Optics system. Recently, Fast Defocus (FADE), a method which measures the coherence time from defocus fluctuations in a small telescope introduced by atmospheric turbulence has been presented. In this work, FADE was implemented for the Nasmyth Adaptive Optics System (NAOS) of the VLT's UT4 to demonstrate suitability for large scale telescopes. Estimates of the coherence time for an examplary set of AO loop data were compared to results obtained with the DIMM and MASS instruments, showing good agreement which justify a future in depth analysis for large AO loop data samples provided by NAOS as well as the VLT's Spectro-Polarimetric High-contrast Exoplanet Research (SPHERE) instrument.

  15. Amplitude fading of simultaneous transionospheric L-band and VHF signals received at the geomagnetic equator

    NASA Technical Reports Server (NTRS)

    Sessions, W. B.

    1972-01-01

    At Ancon, Peru, simultaneous observations of 1550-MHz and 136-MHz signals from the ATS 5 and Intelsat-1 spacecraft showed ionospheric fading as great as 27 db at 136 MHz and 6 db at 1550 MHZ. The observations were made on 48 days during the 1970 autumnal and 1971 vernal equinox periods. Comparison of the two frequencies, in respect to rates and depths of fades, is made. Statistical distributions of the received signal levels during ionospheric scintillation occurrences are presented which may be of use to communications system engineers with operational requirements in the equatorial regions. The distributions show that during expected periods of scintillation, the L band signal typically falls 1.1 db below the median for 1.0 percent of the time, and the VHF signal falls 11.5 db below the median for 1.0 percent of the time.

  16. Cumulative fade statistics and prediction methods associated with the COMSTAR beacon signal at 28.56 GHz

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1978-01-01

    The paper presents cumulative fade statistics for the period April 1977 to March 1978 and reviews the rain attenuation predictive efforts using radar and disdrometer data for the summer of 1977. Attention is given to the receiving and radar systems as well as the disdrometer-raingage system. Discussion of the fade statistics covers the yearly, monthly and time of day statistics. Consideration is given to measured and predicted attenuation events, measured and predicted probability distributions as well as an empirical calibration adjustment. It is noted that in spite of many reasons for noncorrelation, the radar results do correlate well. Finally, it is concluded that the results demonstrate the utility of using radar coupled with disdrometer measurements for predicting individual fade events as well as long term fade distributions associated with satellite communications through rain.

  17. Advanced Communications Technology Satellite (ACTS) Fade Compensation Protocol Impact on Very Small-Aperture Terminal Bit Error Rate Performance

    NASA Technical Reports Server (NTRS)

    Cox, Christina B.; Coney, Thom A.

    1999-01-01

    The Advanced Communications Technology Satellite (ACTS) communications system operates at Ka band. ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of an analysis characterizing the improvement in VSAT performance provided by this protocol. The metric for performance is VSAT bit error rate (BER) availability. The acceptable availability defined by communication system design specifications is 99.5% for a BER of 5E-7 or better. VSAT BER availabilities with and without rain fade compensation are presented. A comparison shows the improvement in BER availability realized with rain fade compensation. Results are presented for an eight-month period and for 24 months spread over a three-year period. The two time periods represent two different configurations of the fade compensation protocol. Index Terms-Adaptive coding, attenuation, propagation, rain, satellite communication, satellites.

  18. Study on capacity fading of 18650 type LiCoO2-based lithium ion batteries during storage

    NASA Astrophysics Data System (ADS)

    Zheng, Liu-Qun; Li, Shu-Jun; Zhang, Deng-Feng; Lin, Hai-Jun; Miao, Yan-Yue; Chen, Shou-Wei; Liu, Hai-Bin

    2015-05-01

    The capacity fading of LiCoO2-based lithium ion batteries during storage was studied. The discharging capacity fading is attributed to the decreasing in the charging capacity at the constant current stage. After 300 cycles, the ratio of the charging capacity of batteries at the constant current stage to the total charging capacity decreases from 87.2 to 71.2%. The bounce-back voltage is closely related to the internal resistance when the battery is discharged to the cut-off voltage of 3.0 V. Batteries were disassembled in the fully discharged state, and then a assembled again in order to deeply understand the causes of the capacity fading of the cathode and anode. The results shows that the SEI film thickness increasing, breaking or repairing process at the anode could be responsible for the high bounce-back voltage, the increase of the internal resistance and the capacity fading during storage.

  19. Restraint fading and the development of alternative behaviour in the treatment of self-restraint and self-injury.

    PubMed

    Lerman, D C; Iwata, B A; Smith, R G; Vollmer, T R

    1994-04-01

    Restraint fading and differential reinforcement were used to reduce the self-injurious behaviour (SIB) and self-restraint of a profoundly retarded man. The variables maintaining both behaviours could not be identified via pre-treatment functional analysis; however, self-restraint exerted at least some stimulus control over SIB. In Phase 1, the subject's topography of self-restraint (wrapping arms in shirt) was replaced with another topography (wrapping wrists in towel) that could be more easily faded to a headband. However, the subject's restraints could not be completely faded, and any movement was accompanied by SIB; thus, in Phase 2, a compliance training procedure was implemented to reduce his SIB while increasing time out of restraint. In Phase 3, the subject was taught to mand for edibles during training sessions. Results indicated that restraint fading combined with the development of alternative behaviour could be an effective treatment procedure for those who engage in both self-restraint and SIB.

  20. Design of a 40/50 GHz satellite ground station for fade mitigation experiments

    NASA Astrophysics Data System (ADS)

    Koudelka, O.; Schmidt, M.; Ebert, J.

    2013-05-01

    Due to the increasing demand in satellite capacity, driven by applications such as high-definition television (HDTV), 3D-TV and interactive broadband services, higher frequency bands will have to be exploited. The capacity on Ku-band is already becoming scarce and Ka-band systems are more commonly used. It can be expected that 40 and 50 GHz (Q and V band) will have to be used in the future. At these frequencies the wave propagation effects have a significant impact on the performance. The traditional approach of implementing large fade margins in the system design is not suitable as it leads to expensive ground terminals. Fade mitigation by adaptive coding and modulation (ACM) is a cost-efficient method. To investigate the Q/V-band for future commercial exploitation, ESA's ALPHASAT satellite will provide experimental payloads for communications and wave propagation experiments. In Graz a Q/V-band ground station is currently under development. It will be equipped with a 3 m tracking antenna, a 50 W Klystron amplifier and a 290 K LNA. Fade mitigation experiments will be conducted, initially using DVB-S2 modems which allow to vary the modulation scheme, the Forward Error Correction code and the symbol rate under control of the ACM computer. In addition, uplink power control can be combined with the ACM methods. A specially developed signal analyser provides precise measurement of the signal/noise ratio. In addition, propagation data will be available from a beacon receiver, also developed by Joanneum Research. Important goals of the experiment are to investigate the reliability of links under realistic operating conditions using ACM and to develop efficient ACM and signal/noise ratio measurement algorithms which can be later implemented in optimised modems for Q/V-band. The paper describes the ground station design and addresses the planned fade mitigation experiments.

  1. FCT and Delay Fading for Elopement with a Child with Autism.

    PubMed

    Stevenson, Maria T; Ghezzi, Patrick M; Valenton, Kymmo G

    2016-06-01

    Nearly half of children with autism have eloped from their caregivers. In assessing elopement, the initial functional analytic results of this case study found positive reinforcement in the form of attention and access to tangibles were the maintaining variables. Functional communication training (FCT) in combination with delay fading was utilized to increase communication and decrease elopement. Results indicated that communication was consistent, elopement remained low, and the child learned to wait. PMID:27606247

  2. Using reinforcer pairing and fading to increase the milk consumption of a preschool child.

    PubMed

    Tiger, Jeffrey H; Hanley, Gregory P

    2006-01-01

    The present study replicates and extends previous research on the treatment of food selectivity by implementing pairing and fading procedures to increase a child's milk consumption during regularly scheduled preschool meals. The treatment involved mixing a small amount of chocolate syrup into a glass of milk and gradually eliminating the chocolate. The procedure and data collection were implemented by preschool teachers and resulted in increased milk drinking at school, which was maintained at home. PMID:17020222

  3. Stabilization of semilinear heat equations, with fading memory, by boundary feedbacks

    NASA Astrophysics Data System (ADS)

    Munteanu, Ionuţ

    2015-07-01

    In this paper, we design stabilizing Dirichlet boundary feedback laws for heat equations with fading memory. The linear finite-dimensional controllers are easily manageable from the computational point of view, because of their simple feedback form, involving only the first N ∈ N eigenfunctions of the Laplace operator. Two examples are provided at the end of the paper, in order to illustrate the acquired results.

  4. Apparatus and Method for Elimination of Polarization-Induced Fading in Fiber-optic Sensor System

    NASA Technical Reports Server (NTRS)

    Chan, Hon Man (Inventor); Parker, Jr., Allen R. (Inventor)

    2015-01-01

    The invention is an apparatus and method of eliminating polarization-induced fading in interferometric fiber-optic sensor system having a wavelength-swept laser optical signal. The interferometric return signal from the sensor arms are combined and provided to a multi-optical path detector assembly and ultimately to a data acquisition and processing unit by way of a switch that is time synchronized with the laser scan sweep cycle.

  5. All known hot RCB stars are fading fast over the last century

    NASA Astrophysics Data System (ADS)

    Schaefer, Bradley E.

    2016-08-01

    The R Coronae Borealis (RCB) stars are cool supergiants that display irregular and deep dips in their light curves, caused by dust formation. There are four known hot RCB stars (DY Cen, MV Sgr, V348 Sgr, and HV 2671), with surface temperatures of 15 000-25 000 K, and prior work has suggested that three of these have secular fading in brightness. I have tested this result by measuring century-long light curves in the Johnson B band with modern comparison star magnitudes, and I have extended this by measuring many magnitudes over a wide time range as well as for the fourth hot RCB star. In all four cases, the B band magnitude of the maximum light is now fast fading. The fading rates (in units of magnitudes per century) are 2.5 for DY Cen after 1960, 1.3 for MV Sgr, 1.3 for V348 Sgr, and 0.7 for HV 2671. This secular fading is caused by the expected evolution of the star across the top of the Hertzsprung-Russell (HR) diagram at constant luminosity, as the temperature rises and the bolometric correction changes. For DY Cen, the brightness at maximum light is rising from 1906 to 1932, and this is caused by the temperature increase from near 5800 to 7500 K. Before 1934, DY Cen had frequent dust dips, while after 1934 there are zero dust dips, so there is some apparent connection between the rising temperature and the formation of the dust. Thus, we have watched DY Cen evolve from an ordinary RCB star up to a hot RCB star and now appearing as an extreme helium star, all in under one century.

  6. Fade Dynamics and its Evolution: The Other Part of the ACTS Rain Prediction Model

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1997-01-01

    The inception of the Advanced Communication Technology Satellite (ACTS) Project has required a similarly advanced statistical mathematical modeling formalism to describe the behavior of the 30/20 GHz links emanating to and from the earth terminals through the deleterious effects of the earth's atmosphere. The resulting ACTS Rain Attenuation Prediction Model has been thoroughly described in (Manning). In the present paper, the basic rudiments of this model will be reviewed; Section 1 covers the static or time-independent portion of the model and Section 2 covers the dynamic or time-dependent portion. The results of Section 2 are then applied to a new approximate solution of the famous problem of the time duration tau of a fade of a random process below some threshold. This is known as the fade duration. The new approximate solution was published in Russian (Denisenko) and, unfortunately, was never published into English. Hence, this work is restated following (Denisenko) in Section 3 which is immediately applied to the random rain fade process. The results for all five ACTS propagation sites as well as Tampa, FL are then given.

  7. Fade Dynamics and Its Evolution: The Other Part of the Acts Rain Prediction Model

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1997-01-01

    The inception of the Advanced Communication Technology Satellite (ACTS) Project has required as similarly advanced statistical mathematical modeling formalism to describe the behavior of the 30/20 GHz links emanating to and from the earth terminals through the deleterious effects of the earth's atmosphere. The resulting ACTS Rain Attenuation Prediction Model has been thoroughly described in [Manning, 1990]. In the present paper, the basic rudiments of this model will be reviewed; Section 1 covers the static or time-independent portion of the model and Section 2 covers the dynamic of time-dependent portion. The results of Section 2 are then applied to a new approximate solution of the famous problem of the time duration tau of a fade of random process below some threshold. This is known as the fade duration. The new approximate solution was published in Russian [Denisenko] and, unfortunately, was never published into English. Hence, this work is restated following [Denisenko] in Section 3 which is immediately applied to the random rain fade process. The results for all five ACTS propagation sites as well as Tampa, FL are then given.

  8. Mitigating voltage fade in cathode materials by improving the atomic level uniformity of elemental distribution.

    PubMed

    Zheng, Jianming; Gu, Meng; Genc, Arda; Xiao, Jie; Xu, Pinghong; Chen, Xilin; Zhu, Zihua; Zhao, Wenbo; Pullan, Lee; Wang, Chongmin; Zhang, Ji-Guang

    2014-05-14

    Lithium- and manganese-rich (LMR) layered-structure materials are very promising cathodes for high energy density lithium-ion batteries. However, their voltage fading mechanism and its relationships with fundamental structural changes are far from being well understood. Here we report for the first time the mitigation of voltage and energy fade of LMR cathodes by improving the atomic level spatial uniformity of the chemical species. The results reveal that LMR cathodes (Li[Li0.2Ni0.2M0.6]O2) prepared by coprecipitation and sol-gel methods, which are dominated by a LiMO2 type R3̅m structure, show significant nonuniform Ni distribution at particle surfaces. In contrast, the LMR cathode prepared by a hydrothermal assisted method is dominated by a Li2MO3 type C2/m structure with minimal Ni-rich surfaces. The samples with uniform atomic level spatial distribution demonstrate much better capacity retention and much smaller voltage fade as compared to those with significant nonuniform Ni distribution. The fundamental findings on the direct correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials may also guide the design of other energy storage materials with enhanced stabilities.

  9. Dynamic rain fade compensation techniques for the advanced communications technology satellite

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1992-01-01

    The dynamic and composite nature of propagation impairments that are incurred on earth-space communications links at frequencies in and above the 30/20 GHz Ka band necessitate the use of dynamic statistical identification and prediction processing of the fading signal in order to optimally estimate and predict the levels of each of the deleterious attenuation components. Such requirements are being met in NASA's Advanced Communications Technology Satellite (ACTS) project by the implementation of optimal processing schemes derived through the use of the ACTS Rain Attenuation Prediction Model and nonlinear Markov filtering theory. The ACTS Rain Attenuation Prediction Model discerns climatological variations on the order of 0.5 deg in latitude and longitude in the continental U.S. The time-dependent portion of the model gives precise availability predictions for the 'spot beam' links of ACTS. However, the structure of the dynamic portion of the model, which yields performance parameters such as fade duration probabilities, is isomorphic to the state-variable approach of stochastic control theory and is amenable to the design of such statistical fade processing schemes which can be made specific to the particular climatological location at which they are employed.

  10. Fading reduction in a phase optical time-domain reflectometer with multimode sensitive fiber

    NASA Astrophysics Data System (ADS)

    Alekseev, A. E.; Vdovenko, V. S.; Gorshkov, B. G.; Potapov, V. T.; Simikin, D. E.

    2016-09-01

    In the present paper we propose a novel type of a coherent phase-sensitive optical time-domain reflectometer (OTDR) that utilizes a multimode optical fiber as a sensitive element and is capable of considerable reduction of signal fading. Elimination of OTDR signal fading consequently removes randomly occurring insensitivity of the fiber regions to an external phase action. The backscattered light field at the input of OTDR sensitive multimode optical fiber is represented by a speckle-like pattern, due to a so called modal noise phenomenon. This speckle pattern randomly changes when an optical probe pulse propagates in the fiber line. The backscattered field intensity in every single speckle changes in time statistically independently from the intensity change in every other speckle remote enough from the first one. Thus, on the output of a multimode sensitive fiber, there exist several statistically independent reflectograms, and every single reflectogram contains the same information about external action. The joint independent analysis of these reflectograms can result in reduced or complete fading elimination.

  11. Role of Manganese Deposition on Graphite in the Capacity Fading of Lithium Ion Batteries.

    PubMed

    Vissers, Daniel R; Chen, Zonghai; Shao, Yuyan; Engelhard, Mark; Das, Ujjal; Redfern, Paul; Curtiss, Larry A; Pan, Baofei; Liu, Jun; Amine, Khalil

    2016-06-01

    Lithium ion batteries utilizing manganese-based cathodes have received considerable interest in recent years for their lower cost and more favorable environmental friendliness relative to their cobalt counterparts. However, Li ion batteries using these cathodes combined with graphite anodes suffer from severe capacity fading at high operating temperatures. In this paper, we report on how the dissolution of manganese impacts the capacity fading within the Li ion batteries. Our investigation reveals that the manganese dissolves from the cathode, transports to the graphite electrode, and deposits onto the outer surface of the innermost solid-electrolyte interphase layer, which is known to be a mixture of inorganic salts (e.g., Li2CO3, LiF, and Li2O). In this location, the manganese facilitates the reduction of the electrolyte and the subsequent formation of lithium-containing products on the graphite, which removes lithium ions from the normal operation of the cell and thereby induces the severe capacity fade. PMID:27152912

  12. Presynaptic snake beta-neurotoxins produce tetanic fade and endplate potential run-down during neuromuscular blockade in mouse diaphragm.

    PubMed

    Wilson, H I; Nicholson, G M

    1997-11-01

    The present study investigated the ability of a number of presynaptic snake neurotoxins (snake beta-neurotoxins) to produce nerve-evoked train-of-four fade, tetanic fade and endplate potential run-down during the development of neuromuscular blockade in the isolated mouse phrenic-hemidiaphragm nerve-muscle preparation. All the snake beta-neurotoxins tested, with the exception of notexin, produced train-of-four and tetanic fade of nerve-evoked isometric muscle contractions. Train-of-four fade was not present during the initial depressant or facilitatory phases of muscle tension produced by the snake beta-neurotoxins but developed progressively during the final depressant phase that precedes complete neuromuscular blockade. The 'non-neurotoxic' bovine pancreatic phospholipase A2 and the 'low-toxicity' phospholipase A2 from Naja naja atra venom failed to elicit train-of-four fade, indicating that the phospholipase activity of the snake beta-neurotoxins is not responsible for the development of fade. Intracellular recording of endplate potentials (EPPs) elicited by nerve-evoked trains of stimuli showed a progressive run-down in EPP amplitude during the train following incubation with all snake beta-neurotoxins except notexin. Again this run-down in EPP amplitude was confined to the final depressant phase of snake beta-neurotoxin action. However when EPP amplitude fell to near uniquantal levels (< 3 mV) the extent of toxin induced-fade was reduced. Unlike postjunctional snake alpha-neurotoxins, prejunctional snake beta-neurotoxins interfere with acetylcholine release at the neuromuscular junction during the development of neuromuscular blockade. This study provides further support for the hypothesis that fade in twitch and tetanic muscle tension is due to an underlying rundown in EPP amplitude resulting from a prejunctional alteration of transmitter release rather than a use-dependent block of postjunctional nicotinic receptors.

  13. Relationships between block-of-twitch and train-of-four fade in the mouse phrenic nerve-diaphragm preparation.

    PubMed

    Storella, R J; Slomowitz, S A; Rosenberg, H

    1991-04-01

    The relationships between the block-of-twitch and train-of-four fade in the presence of nondepolarizing neuromuscular blocking drugs (d-tubocurarine, vecuronium and pancuronium) were examined in vitro by measuring the contractile tension from mouse phrenic nerve-diaphragm preparations. The slope of the block/fade relationship differed between onset of and recovery from neuromuscular block following single doses of d-tubocurarine, vecuronium or pancuronium. Decreasing the dose of d-tubocurarine or using a divided dose technique to accelerate onset (i.e., priming) increased the amount of fade for a given amount of block. In addition, the block/fade relationships for cumulative dosing and sequential dilution were the same when measurements were made at steady-state for several doses. It is concluded that the block/fade relationship in the mouse phrenic nerve-diaphragm preparation is variable, and is related to the time course of the neuromuscular block. In addition, the block/fade relationships for d-tubocurarine, vecuronium and pancuronium did not differ when determined at steady-state.

  14. Compilation and Analysis of 20 and 30 GHz Rain Fade Events at the ACTS NASA Ground Station: Statistics and Model Assessment

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1996-01-01

    The purpose of the propagation studies within the ACTS Project Office is to acquire 20 and 30 GHz rain fade statistics using the ACTS beacon links received at the NGS (NASA Ground Station) in Cleveland. Other than the raw, statistically unprocessed rain fade events that occur in real time, relevant rain fade statistics derived from such events are the cumulative rain fade statistics as well as fade duration statistics (beyond given fade thresholds) over monthly and yearly time intervals. Concurrent with the data logging exercise, monthly maximum rainfall levels recorded at the US Weather Service at Hopkins Airport are appended to the database to facilitate comparison of observed fade statistics with those predicted by the ACTS Rain Attenuation Model. Also, the raw fade data will be in a format, complete with documentation, for use by other investigators who require realistic fade event evolution in time for simulation purposes or further analysis for comparisons with other rain fade prediction models, etc. The raw time series data from the 20 and 30 GHz beacon signals is purged of non relevant data intervals where no rain fading has occurred. All other data intervals which contain rain fade events are archived with the accompanying time stamps. The definition of just what constitutes a rain fade event will be discussed later. The archived data serves two purposes. First, all rain fade event data is recombined into a contiguous data series every month and every year; this will represent an uninterrupted record of the actual (i.e., not statistically processed) temporal evolution of rain fade at 20 and 30 GHz at the location of the NGS. The second purpose of the data in such a format is to enable a statistical analysis of prevailing propagation parameters such as cumulative distributions of attenuation on a monthly and yearly basis as well as fade duration probabilities below given fade thresholds, also on a monthly and yearly basis. In addition, various subsidiary

  15. English Channel

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The cloud covered earthscape of Northern Europe demonstrates the difficulty of photographing this elusive subject from space. The English Channel (51.0N, 1.5E) separating the British Islands from Europe is in the center of the scene. The white cliffs of Dover on the SE coast of the UK, the Thames River estuary and a partial view of the city of London can be seen on the north side of the Channel while the Normandy coast of France is to the south.

  16. Beamforming transmission in IEEE 802.11ac under time-varying channels.

    PubMed

    Yu, Heejung; Kim, Taejoon

    2014-01-01

    The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes.

  17. Beamforming transmission in IEEE 802.11ac under time-varying channels.

    PubMed

    Yu, Heejung; Kim, Taejoon

    2014-01-01

    The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes. PMID:25152927

  18. Beamforming Transmission in IEEE 802.11ac under Time-Varying Channels

    PubMed Central

    2014-01-01

    The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes. PMID:25152927

  19. BER Performance of Decode-and-Forward Relaying Using Equal-Gain Combining over Rayleigh Fading Channels

    NASA Astrophysics Data System (ADS)

    Vo Nguyen, Bao Quoc; Kong, Hyung Yun

    This paper provides a closed form expression for calculating the bit error rate of the decode-and-forward relay protocol that uses equal-gain combining (EGC) at the destination with an arbitrary number of relays. We have shown that EGC technique for decode-and-forward relay scheme offers remarkable diversity advantage over direct transmission. In addition, we also study the impact of combining techniques on the performance of the system by comparing a system that uses EGC to one that uses maximum ratio combining (MRC) & selection combining (SC). Simulations are performed to confirm our theoretical analysis.

  20. Outage performance of multihop free-space optical communication system over exponentiated Weibull fading channels with nonzero boresight pointing errors

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-xia; Wang, Ping; Cao, Tian

    2016-09-01

    The outage performance of the multihop free-space optical (FSO) communication system with decode-and-forward (DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull (EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.

  1. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, Victor R.

    1988-01-01

    The geomorphology of Mars is discussed, focusing on the Martian channels. The great flood channels of Mars, the processes of channel erosion, and dendritic channel networks, are examined. The topography of the Channeled Scabland region of the northwestern U.S. is described and compared to the Martian channels. The importance of water in the evolution of the channel systems is considered.

  2. Nonlinear channelizer.

    PubMed

    In, Visarath; Longhini, Patrick; Kho, Andy; Neff, Joseph D; Leung, Daniel; Liu, Norman; Meadows, Brian K; Gordon, Frank; Bulsara, Adi R; Palacios, Antonio

    2012-12-01

    The nonlinear channelizer is an integrated circuit made up of large parallel arrays of analog nonlinear oscillators, which, collectively, serve as a broad-spectrum analyzer with the ability to receive complex signals containing multiple frequencies and instantaneously lock-on or respond to a received signal in a few oscillation cycles. The concept is based on the generation of internal oscillations in coupled nonlinear systems that do not normally oscillate in the absence of coupling. In particular, the system consists of unidirectionally coupled bistable nonlinear elements, where the frequency and other dynamical characteristics of the emergent oscillations depend on the system's internal parameters and the received signal. These properties and characteristics are being employed to develop a system capable of locking onto any arbitrary input radio frequency signal. The system is efficient by eliminating the need for high-speed, high-accuracy analog-to-digital converters, and compact by making use of nonlinear coupled systems to act as a channelizer (frequency binning and channeling), a low noise amplifier, and a frequency down-converter in a single step which, in turn, will reduce the size, weight, power, and cost of the entire communication system. This paper covers the theory, numerical simulations, and some engineering details that validate the concept at the frequency band of 1-4 GHz.

  3. HUBBLE STAYS ON TRAIL OF FADING GAMMA-RAY BURST FIREBALL

    NASA Technical Reports Server (NTRS)

    2002-01-01

    A Hubble Space Telescope image of the fading fireball from one of the universe's most mysterious phenomena, a gamma-ray burst. Though the visible component has faded to 1/500th its brightness (27.7 magnitude) from the time it was first discovered by ground- based telescopes last March (the actual gamma-ray burst took place on February 28), Hubble continues to clearly see the fireball and discriminated a surrounding nebulosity (at 25th magnitude) which is considered a host galaxy. The continued visibility of the burst, and the rate of its fading, support theories that the light from a gamma-ray burst is an expanding relativistic (moving near the speed of light) fireball, possibly produced by the collision of two dense objects, such as an orbiting pair of neutron stars. If the burst happened nearby, within our own galaxy, the resulting fireball should have had only enough energy to propel it into space for a month. The fact that this fireball is still visible after six months means the explosion was truly titanic and, to match the observed brightness, must have happened at the vast distances of galaxies. The energy released in a burst, which can last from a fraction of a second to a few hundred seconds, is equal to all of the Sun's energy generated over its 10 billion year lifetime. The false-color image was taken Sept. 5, 1997 with the Space Telescope Imaging Spectrograph. Credit: Andrew Fruchter (STScI), Elena Pian (ITSRE-CNR), and NASA

  4. Characterization of ten microsatellite loci in midget faded rattlesnake (Crotalus oreganus concolor)

    USGS Publications Warehouse

    Oyler-McCance, Sara J.; Parker, Joshua M.

    2010-01-01

    Primers for 10 microsatellite loci were developed for midget faded rattlesnake (Crotalus oreganus concolor), a small bodied subspecies of the Western Rattlesnake, which is found in the Colorado Plateau of eastern Utah, western Colorado and southwestern Wyoming. In a screen of 23 individuals from the most northern portion of the subspecies range in southwestern Wyoming, the 10 loci were found to have levels of variability ranging from 4 to 11 alleles. No loci were found to be linked, although one locus revealed significant departures from Hardy–Weinberg equilibrium. These microsatellite loci will be applicable for population genetic analyses, which will ultimately aid in management efforts for this rare subspecies of rattlesnake.

  5. Compressive sensing based Bayesian sparse channel estimation for OFDM communication systems: high performance and low complexity.

    PubMed

    Gui, Guan; Xu, Li; Shan, Lin; Adachi, Fumiyuki

    2014-01-01

    In orthogonal frequency division modulation (OFDM) communication systems, channel state information (CSI) is required at receiver due to the fact that frequency-selective fading channel leads to disgusting intersymbol interference (ISI) over data transmission. Broadband channel model is often described by very few dominant channel taps and they can be probed by compressive sensing based sparse channel estimation (SCE) methods, for example, orthogonal matching pursuit algorithm, which can take the advantage of sparse structure effectively in the channel as for prior information. However, these developed methods are vulnerable to both noise interference and column coherence of training signal matrix. In other words, the primary objective of these conventional methods is to catch the dominant channel taps without a report of posterior channel uncertainty. To improve the estimation performance, we proposed a compressive sensing based Bayesian sparse channel estimation (BSCE) method which cannot only exploit the channel sparsity but also mitigate the unexpected channel uncertainty without scarifying any computational complexity. The proposed method can reveal potential ambiguity among multiple channel estimators that are ambiguous due to observation noise or correlation interference among columns in the training matrix. Computer simulations show that proposed method can improve the estimation performance when comparing with conventional SCE methods.

  6. Statistical characterization of the dynamic human body communication channel at 45 MHz.

    PubMed

    Nie, Zedong; Ma, Jingjing; Chen, Hong; Wang, Lei

    2013-01-01

    The dynamic human body communication (HBC) propagation channel at 45 MHz was statistical characterized in this paper. A large amount of measurement data has been gathered in practical environment with real activities -treadmill running at different speeds in a lab room. The received power between two lower legs was acquired from three volunteers, with more than 60,000 snap shot of data in total. The statistical analyses confirmed that the HBC propagation channel at 45 MHz followed the Gamma and Lognormal distributions at the slower (2 km/h and 4 km/h) and faster (6 km/h and 8 km/h) running activities, respectively. The channel is insensitive to body motion with the maximum average fade duration is 0.0413 s and the most averaging bad channel duration time being less than 60 ms with the percentage of the bad channel duration time being less than 4.35%.

  7. The fading affect bias in the context of emotion activation level, mood, and personal theories of emotion change.

    PubMed

    Ritchie, Timothy; Skowronski, John J; Hartnett, Jessica; Wells, Brett; Walker, W Richard

    2009-05-01

    The intensity of emotions associated with memory of pleasant events generally fades more slowly across time than the intensity of emotions associated with memory of unpleasant events, a phenomenon known as the fading affect bias (FAB). Four studies examined variables that might account for, or moderate, the bias. These included the activation level of the emotions, individual differences in dispositional mood, and participant expectations of emotion change across time. Results suggest that (a) although emotion activation level was related to overall fading of affect, it was unrelated to the FAB; (b) dispositional mood moderated the FAB, but could not fully account for it; and (c) although participants' predictions of event-related emotion change across time were somewhat veridical, the FAB emerged even when these predictions were accounted for statistically. Methodological and theoretical implications for research on the affect associated with autobiographical events are discussed.

  8. This Too Shall Pass: Evidence of Coping and Fading Emotion in African Americans' Memories of Violent and Nonviolent Death.

    PubMed

    Henderson, Dawn X; Bond, Gary D; Alderson, Courtney J; Walker, W Richard

    2015-01-01

    Two studies examined African Americans essays on coping with violent and nonviolent death and fading affect bias. Essays from 101 African Americans were coded for psychological resolution (resolved or unresolved) and for type of death (violent or nonviolent). Linguistic analyses were used to examine the experience of loss and coping methods. Religious coping was important for nonviolent death events while social support and emotion (e.g., crying) were themes that emerged for violent death events. For unresolved violent death events, dissociation was a common theme. The perceived change in the emotional intensity of the events was examined and revealed that the negative emotion showed evidence of substantial fading. Overall, these results suggest religious coping, social support and sharing enhance coping among African American participants. These processes can help negative affect associated with death events fade, allowing for psychological resolution, healing, and resilience.

  9. A Short Note on the Derivation of the Atmospheric Transfer Function for a Communications Channel and its Connection to Associated Propagation Parameters

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    2004-01-01

    The systems engineering description of a wideband communications channel is provided which is based upon the fundamental propagation aspects of the problem. In particular, the well known time variant description of a channel is formulated from the basic multiple scattering processes that occur in a random propagation medium. Such a connection is required if optimal processing methods are to be applied to mitigate the deleterious random fading and multipathing of the channel. An example is given which demonstrates how the effective bandwidth of the channel is diminished due to atmospheric propagation impairments.

  10. Sentence Recognition Prediction for Hearing-impaired Listeners in Stationary and Fluctuation Noise With FADE

    PubMed Central

    Schädler, Marc René; Warzybok, Anna; Meyer, Bernd T.; Brand, Thomas

    2016-01-01

    To characterize the individual patient’s hearing impairment as obtained with the matrix sentence recognition test, a simulation Framework for Auditory Discrimination Experiments (FADE) is extended here using the Attenuation and Distortion (A+D) approach by Plomp as a blueprint for setting the individual processing parameters. FADE has been shown to predict the outcome of both speech recognition tests and psychoacoustic experiments based on simulations using an automatic speech recognition system requiring only few assumptions. It builds on the closed-set matrix sentence recognition test which is advantageous for testing individual speech recognition in a way comparable across languages. Individual predictions of speech recognition thresholds in stationary and in fluctuating noise were derived using the audiogram and an estimate of the internal level uncertainty for modeling the individual Plomp curves fitted to the data with the Attenuation (A-) and Distortion (D-) parameters of the Plomp approach. The “typical” audiogram shapes from Bisgaard et al with or without a “typical” level uncertainty and the individual data were used for individual predictions. As a result, the individualization of the level uncertainty was found to be more important than the exact shape of the individual audiogram to accurately model the outcome of the German Matrix test in stationary or fluctuating noise for listeners with hearing impairment. The prediction accuracy of the individualized approach also outperforms the (modified) Speech Intelligibility Index approach which is based on the individual threshold data only. PMID:27604782

  11. RF power fading mitigation for an IMDD multicarrier LR-PON.

    PubMed

    Chen, You-Wei; Lai, Tsan-Ning; Chang, Mu-Fan; Feng, Kai-Ming

    2016-08-22

    In an intensity-modulation direct-detection (IMDD) orthogonal frequency division multiplexing (OFDM) signal format, radio frequency (RF) power fading produces non-uniform receiving performance among the subcarriers due to chromatic dispersion. Hence each subscriber experiences distinct quality of service (QoS) in conventional frequency division multiple access (FDMA). In this paper, a multicarrier code division multiple access (MC-CDMA) signal along with multicode interference (MCI) cancellation process is proposed and experimentally demonstrated to enhance the receiving performance in an IMDD long reach passive optical network (LR-PON). With the proposed scheme, the receiving performance of each subcarrier can be equalized so that a universal transmitter design at central office (CO) can support all the subscribers with their locations ranging from back-to-back to 100 km. Our experimental results also reveal that, even under 20 dB RF power fading, the proposed scheme can still provide over 21.7 dB power budget and only approximately 2 dB sensitivity deviation is observed in an IMDD LR-PON system.

  12. TOPEX El Nino/La Nina -La Nina Begins to Fade, April 7, 1999

    NASA Technical Reports Server (NTRS)

    1999-01-01

    The cold pool of water in the Pacific known as 'La Nina' is beginning to fade, but ocean conditions have not returned to normal, according to scientists studying new images from the U.S.-French TOPEX/Poseidon satellite.

    New imagery of sea-surface heights taken this month by the ocean-observing satellite show cooler temperatures and lower sea levels across the equatorial Pacific Ocean (seen in blue and purple in the center of the image) are diminishing, which indicates that the equatorial Pacific is slowly returning to normal.

    However, in the north and south Pacific Ocean, temperatures and sea level remain high (seen in red and white), a pattern that began many months ago. In a nutshell, this means that although La Nina is fading, heat distribution in the Pacific Ocean remains dramatically out of balance.

    The TOPEX/Poseidon mission is managed by the Jet Propulsion Laboratory for NASA s Office of Earth Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA.

    For more information, please visit the TOPEX/Poseidon project web page at http://topex-www.jpl.nasa.gov

  13. The mechanism of capacity fade of rechargeable alkaline manganese dioxide zinc cells

    NASA Astrophysics Data System (ADS)

    Shen, Yuwei; Kordesch, Karl

    Recent experiments showed, that in contrast to traditional opinion, if the cathode was protected by anode limitation the capacity fade of Rechargeable Alkaline Manganese Dioxide Zinc (RAM™) cells was not caused by the EMD cathode, but by the gelled zinc anode. The key is the electrolyte. The cathode competition for the electrolyte and the increasing requirement of chemically formed ZnO for more electrolyte caused an electrolyte deficiency at the front face of the anode and finally caused precipitation of zincate and passivation of zinc. The crust is a mixed material of precipitation and passivation products. The low solubility ZnO is formed by decomposition of electrochemically generated zincate ions [Zn(OH) 4] 2- and also by recombination of zinc with oxygen during overcharge. The progressively thickened "crust" at the front face of the anode increases the resistance, then finally causes the cell to fade. The crusting is a redistribution of active material and electrolyte between the front and rear of the cylindrical gelled zinc anode. More electrolyte and proper charging can delay such a "crusting" phenomenon.

  14. Athermal fading of luminescence in Al2 O3 ceramic substrates

    NASA Astrophysics Data System (ADS)

    Terry, Ian; Kouroukla, Eftychia; Bailiff, Ian K.

    2015-03-01

    Retrospective dosimetry aims to reconstruct ionising radiation dose to populations following a radiological incident using materials not designed for that purpose. Sintered alumina ceramic can function as a dosimeter with its luminescence properties and related trapped charge storage mechanism. Its widespread use as a substrate in surface mount devices and incorporation in devices such as mobile phones make it a ubiquitous potential dosimeter. We investigated the optically (OSL) and thermally (TL) stimulated luminescence properties of sintered alumina substrates. In contrast to their single crystal analogue developed for personal dosimetry, Al2O3:C, the substrates exhibit a significant loss of trapped charge (fading) within hours following irradiation at RT that seriously limits their utility for dosimetry over an extended timescale. The fading rates of OSL and TL signals of 0402 resistors were analysed under various storage conditions (time and temperature), complemented by a study of their microstructure. The results support a model of athermal loss of trapped charge due to electron tunnelling from trapping states; this contrasting behaviour is attributed to a physical modification of the trap environment arising from the manufacturing process.

  15. RF power fading mitigation for an IMDD multicarrier LR-PON.

    PubMed

    Chen, You-Wei; Lai, Tsan-Ning; Chang, Mu-Fan; Feng, Kai-Ming

    2016-08-22

    In an intensity-modulation direct-detection (IMDD) orthogonal frequency division multiplexing (OFDM) signal format, radio frequency (RF) power fading produces non-uniform receiving performance among the subcarriers due to chromatic dispersion. Hence each subscriber experiences distinct quality of service (QoS) in conventional frequency division multiple access (FDMA). In this paper, a multicarrier code division multiple access (MC-CDMA) signal along with multicode interference (MCI) cancellation process is proposed and experimentally demonstrated to enhance the receiving performance in an IMDD long reach passive optical network (LR-PON). With the proposed scheme, the receiving performance of each subcarrier can be equalized so that a universal transmitter design at central office (CO) can support all the subscribers with their locations ranging from back-to-back to 100 km. Our experimental results also reveal that, even under 20 dB RF power fading, the proposed scheme can still provide over 21.7 dB power budget and only approximately 2 dB sensitivity deviation is observed in an IMDD LR-PON system. PMID:27557210

  16. Advanced communications technology satellite high burst rate link evaluation terminal power control and rain fade software test plan, version 1.0

    NASA Technical Reports Server (NTRS)

    Reinhart, Richard C.

    1993-01-01

    The Power Control and Rain Fade Software was developed at the NASA Lewis Research Center to support the Advanced Communications Technology Satellite High Burst Rate Link Evaluation Terminal (ACTS HBR-LET). The HBR-LET is an experimenters terminal to communicate with the ACTS for various experiments by government, university, and industry agencies. The Power Control and Rain Fade Software is one segment of the Control and Performance Monitor (C&PM) Software system of the HBR-LET. The Power Control and Rain Fade Software automatically controls the LET uplink power to compensate for signal fades. Besides power augmentation, the C&PM Software system is also responsible for instrument control during HBR-LET experiments, control of the Intermediate Frequency Switch Matrix on board the ACTS to yield a desired path through the spacecraft payload, and data display. The Power Control and Rain Fade Software User's Guide, Version 1.0 outlines the commands and procedures to install and operate the Power Control and Rain Fade Software. The Power Control and Rain Fade Software Maintenance Manual, Version 1.0 is a programmer's guide to the Power Control and Rain Fade Software. This manual details the current implementation of the software from a technical perspective. Included is an overview of the Power Control and Rain Fade Software, computer algorithms, format representations, and computer hardware configuration. The Power Control and Rain Fade Test Plan provides a step-by-step procedure to verify the operation of the software using a predetermined signal fade event. The Test Plan also provides a means to demonstrate the capability of the software.

  17. Visual assessment of train-of-four and double burst-induced fade at submaximal stimulating currents.

    PubMed

    Brull, S J; Silverman, D G

    1991-11-01

    The influence of current intensity on visual assessment of fade in response to train-of-four (TOF) and two modes of double-burst stimulation (DBS) was determined to assess the utility of low-current neurostimulation. Each of 150 sets of assessments (in 51 patients) included a mechanographic TOF at 60 mA followed by visual assessments of TOF, DBS3,3 (two minitetanic bursts of three stimuli each), and DBS3,2 (a burst of three followed by a burst of two impulses) at 20, 30, 50, and 60 mA in random order. For the range of mechanographic TOF ratios between 0.41 and 0.70, visual assessment of TOF fade failed to identify fade in 33%, 36%, 44%, and 58% of cases at 20, 30, 50, and 60 mA, respectively. Corresponding false-negative rates for DBS3,3 were 11%, 17%, 36%, and 33%, and for DBS3,2 they were 6%, 6%, 17%, and 28%. Within each method, P less than 0.05 (by Mantel-Haenszel analysis) for a linear trend of increasing accuracy as current decreased. For the range between 0.41 and 0.70, quantitative assessment overestimated the actual ratio at all currents for TOF, at 30, 50, and 60 mA for DBS3,3, and at 50 and 60 mA for DBS3,2 (P less than 0.05 by Wilcoxon signed rank test). At each current tested, DBS was more sensitive in detecting fade visually than TOF. The accuracy of visual fade detection was not influenced significantly by level of observer training. In conclusion, visual assessment of fade by novice and expert observers is improved by testing at low currents.

  18. The Impact of Reading Material's Lexical Accessibility on Text Fading Effects in Children's Reading Performance

    ERIC Educational Resources Information Center

    Nagler, Telse; Lonnemann, Jan; Linkersdörfer, Janosch; Hasselhorn, Marcus; Lindberg, Sven

    2014-01-01

    The "acceleration phenomenon" (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce…

  19. AG Channel Measurement and Modeling Results for Over-Water and Hilly Terrain Conditions

    NASA Technical Reports Server (NTRS)

    Matolak, David W.; Sun, Ruoyu

    2015-01-01

    This report describes work completed over the past year on our project, entitled "Unmanned Aircraft Systems (UAS) Research: The AG Channel, Robust Waveforms, and Aeronautical Network Simulations." This project is funded under the NASA project "Unmanned Aircraft Systems (UAS) in the National Airspace System (NAS)." In this report we provide the following: an update on project progress; a description of the over-freshwater and hilly terrain initial results on path loss, delay spread, small-scale fading, and correlations; complete path loss models for the over-water AG channels; analysis for obtaining parameter statistics required for development of accurate wideband AG channel models; and analysis of an atypical AG channel in which the aircraft flies out of the ground site antenna main beam. We have modeled the small-scale fading of these channels with Ricean statistics, and have quantified the behavior of the Ricean K-factor. We also provide some results for correlations of signal components, both intra-band and inter-band. An updated literature review, and a summary that also describes future work, are also included.

  20. An updated estimate of the number of Jupiter-family comets using a simple fading law

    NASA Astrophysics Data System (ADS)

    Brasser, R.; Wang, J.-H.

    2015-01-01

    It has long been hypothesised that the Jupiter-family comets (JFCs) come from the scattered disc, an unstable planetesimal population beyond Neptune. This viewpoint has been widely accepted, but a few issues remain, the most prominent of which are the total number of visible JFCs with a perihelion distance q < 2.5 AU and the corresponding number of objects in the scattered disc. In this work we give a robust estimate of the number of visible JFCs with q < 2.5 AU and diameter D> 2.3 km based on recent observational data. This is combined with numerical simulations that use a simple fading law applied to JFCs that come close to the Sun. For this we numerically evolve thousands of comets from the scattered disc through the realm of the giant planets and keep track of their number of perihelion passages with perihelion distance q < 2.5 AU, below which the activity is supposed to increase considerably. We can simultaneously fit the JFC inclination and semi-major axis distribution accurately with a delayed power law fading function of the form Φm ∝ (M2 + m2)- k/ 2, where Φm is the visibility, m is the number of perihelion passages with q < 2.5 AU, M is an integer constant, and k is the fading index. We best match both the inclination and semi-major axis distributions when k ~ 1.4, M = 40, and the maximum perihelion distance below which the observational data is complete is qm ~ 2.3 AU. From observational data we calculate that a JFC with diameter D = 2.3 km has a typical total absolute magnitude HT = 10.8, and the steady-state number of active JFCs with diameter D > 2.3 km and q < 2.5 AU is of the order of 300 (but with large uncertainties), approximately a factor two higher than earlier estimates. The increased JFC population results in a scattered disc population of 6 billion objects and decreases the observed Oort cloud to scattered disc population ratio to 13, virtually the same as the value of 12 obtained with numerical simulations.

  1. Supporting Survey Courses with Lecture-Tutorials and Backwards-Faded Scaffolded Inquiry

    NASA Astrophysics Data System (ADS)

    Slater, T. F.; Slater, S. J.

    2013-12-01

    In the course of learning science, it is generally accepted that successful science learning experiences should result in learners developing a meaningful understanding of the nature of science as inquiry where: (i) students are engaged in questions; (ii) students are designing plans to pursue data; and (iii) students are generating and defending conclusions based on evidence they have collected. Few of these learning targets can be effectively reached through a professor-centered, information download lecture. In response to national reform movements calling for professors to adopt teaching strategies and learning environments where non-science majors and future teachers can actively engage in scientific discourse, scholars with the CAPER Center for Astronomy & Physics Education Research have leveraged NSF DUE funding over the last decade to develop and systematically field-test two separate instructional approaches. The first of these is called Lecture-Tutorials (NSF 99077755 and NSF 9952232) . These are self-contained, classroom-ready, collaborative group activities. The materials are designed specifically to be easily integrated into the lecture course and directly address the needs of busy and heavily-loaded teaching faculty for effective, student-centered, classroom-ready materials that do not require a drastic course revision for implementation. Students are asked to reason about difficult concepts, while working in pairs, and to discuss their ideas openly. The second of these is a series of computer-mediated, inquiry learning experiences for non-science majoring undergraduates based upon an inquiry-oriented teaching approach framed by the notions of backwards faded-scaffolding as an overarching theme for instruction (NSF 1044482). Backwards faded-scaffolding is a strategy where the conventional and rigidly linear scientific method is turned on its head and students are first taught how to create conclusions based on evidence, then how experimental design

  2. Using Prompt Fading to Teach Self-Questioning to Fifth Graders with LD: Effects on Reading Comprehension

    ERIC Educational Resources Information Center

    Rouse, Christina A.; Alber-Morgan, Sheila R.; Cullen, Jennifer M.; Sawyer, Mary

    2014-01-01

    Students with LD who struggle with reading comprehension can benefit from instruction on how to read strategically. One strategy that has been demonstrated to increase reading comprehension is self-questioning. In this study, two fifth graders with LD were taught to self-generate questions using a prompt fading procedure. The participants were…

  3. The Use of Nicotine Fading and Self-Monitoring to Reduce Cigarette Smoking: A Non-Aversive Procedure.

    ERIC Educational Resources Information Center

    Brown, Richard A.; Foxx, R. M.

    Several treatment approaches to cigarette smoking were investigated, including a nicotine fading procedure in which subjects changed their cigarette brand each week to one containing progressively less nicotine and tar; a self-monitoring procedure in which subjects plotted their daily intake of nicotine and tar; a combined nicotine…

  4. Comparison of Most-to-Least Prompting to Flexible Prompt Fading for Children with Autism Spectrum Disorder

    ERIC Educational Resources Information Center

    Leaf, Justin B.; Leaf, Jeremy A.; Alcalay, Aditt; Kassardjian, Alyne; Tsuji, Kathleen; Dale, Stephanie; Ravid, Daniel; Taubman, Mitchell; McEachin, John; Leaf, Ronald

    2016-01-01

    This study compared most-to-least prompting to flexible prompt fading for teaching four children with an autism spectrum disorder various expressive tasks. Using a parallel treatment design nested into a multiple probe design, researchers taught each participant how to expressively label six pictures with most-to-least prompting and six pictures…

  5. Identification of Printed Nonsense Words for an Individual with Autism: A Comparison of Constant Time Delay and Stimulus Fading

    ERIC Educational Resources Information Center

    Redhair, Emily

    2011-01-01

    This study compared a stimulus fading (SF) procedure with a constant time delay (CTD) procedure for identification of consonant-vowel-consonant (CVC) nonsense words for a participant with autism. An alternating treatments design was utilized through a computer-based format. Receptive identification of target words was evaluated using a computer…

  6. Identification of Printed Nonsense Words for an Individual with Autism: A Comparison of Constant Time Delay and Stimulus Fading

    ERIC Educational Resources Information Center

    Redhair, Emily I.; McCoy, Kathleen M.; Zucker, Stanley H.; Mathur, Sarup R.; Caterino, Linda

    2013-01-01

    This study compared a stimulus fading (SF) procedure with a constant time delay (CTD) procedure for identification of consonant-vowel-consonant (CVC) nonsense words for a participant with autism. An alternating treatments design was utilized through a computer-based format. Receptive identification of target words was evaluated using a computer…

  7. Effects of Fading Support on Hypertext Navigation and Performance in Student-Centered E-Learning Environments

    ERIC Educational Resources Information Center

    Kester, Liesbeth; Kirschner, Paul A.

    2009-01-01

    Whether fading support for problems affects accuracy of hypertext navigation and problem performance is investigated in this study. In a student-centered e-learning environment conceptual support is added to help domain novices get an overview of the problem domain, while strategic support is provided to help domain novices get insight into the…

  8. Differential reinforcement of alternative behavior and demand fading in the treatment of escape-maintained destructive behavior.

    PubMed

    Piazza, C C; Moes, D R; Fisher, W W

    1996-01-01

    The escape-maintained destructive behavior of a boy with autism was reduced during instructional sequences with differential reinforcement of compliance (DRA), escape extinction without physical guidance, and demand fading. The procedure decreased destructive behaviors to near-zero levels and greatly increased compliance.

  9. Differential Reinforcement of Alternative Behavior and Demand Fading in the Treatment of Escape-Maintained Destructive Behavior.

    ERIC Educational Resources Information Center

    Piazza, Cathleen C.; And Others

    1996-01-01

    A study of an 11-year-old boy with autism and mild mental retardation found that his escape-maintained destructive behavior was reduced during instructional sequences with differential reinforcement of compliance, escape extinction without physical guidance, and demand fading. The procedure decreased destructive behaviors to near-zero levels and…

  10. Effects of Superimposition and Background Fading on the Sight-Word Reading of a Boy with Autism

    ERIC Educational Resources Information Center

    Birkan, Binyamin; McClannahan, Lynn E.; Krantz, Patricia J.

    2007-01-01

    We used a multiple-baseline design across materials to assess the effects of stimulus superimposition and background fading on the sight-word reading skills of a 6-year-old boy with autism. Before the study began, the boy was taught to make verbal responses when shown 15 photographs of physical education activities and equipment. During baseline…

  11. Method for retarding dye fading during archival storage of developed color photographic film. [inert atmosphere

    NASA Technical Reports Server (NTRS)

    Hoover, R. B.; Rhodes, C. M. (Inventor)

    1981-01-01

    Dye fading during archival storage of developed color photographic film is retarded by placing the film in a sealed, opaque vault, introducing a dry, pressurized inert gas into the vault while the latter is vented, and sealing the vault after the air within the vault has been purged and replaced by the inert gas. Preferably, the gas is nitrogen; and the vault is stored at a temperature below room temperature to preserve the color photographic emulsions on the film contained within the vault. For short-term storage, sodium thiocyanate pads charged with water are placed within the vault. For long term storage, the interior of the vault is kept at a low relative humidity.

  12. Compassion fade: affect and charity are greatest for a single child in need.

    PubMed

    Västfjäll, Daniel; Slovic, Paul; Mayorga, Marcus; Peters, Ellen

    2014-01-01

    Charitable giving in 2013 exceeded $300 billion, but why do we respond to some life-saving causes while ignoring others? In our first two studies, we demonstrated that valuation of lives is associated with affective feelings (self-reported and psychophysiological) and that a decline in compassion may begin with the second endangered life. In Study 3, this fading of compassion was reversed by describing multiple lives in a more unitary fashion. Study 4 extended our findings to loss-frame scenarios. Our capacity to feel sympathy for people in need appears limited, and this form of compassion fatigue can lead to apathy and inaction, consistent with what is seen repeatedly in response to many large-scale human and environmental catastrophes.

  13. A novel method for combating dispersion induced power fading in dispersion compensating fiber.

    PubMed

    Lebedev, Alexander; Olmos, J J Vegas; Iglesias, Miguel; Forchhammer, Søren; Monroy, Idelfonso Tafur

    2013-06-01

    We experimentally investigate the performance of 60 GHz double sideband (DSB) radio over fiber (RoF) links that employ dispersion compensating fiber (DCF). Error free transmission of 3 Gbps signals over 1 m of wireless distance is reported. In order to overcome experimentally observed chromatic dispersion (CD) induced power fading of radio frequency (RF) signal, we propose a method for improvement of RF carrier-to-noise (C/N) ratio through introduction of a degree of RF frequency tunability. Overall results improve important aspects of directly modulated RoF systems and demonstrate the feasibility of high carrier frequency and wide bandwidth RF signals delivery in RoF links including DCF fiber. Error free performance that we obtain for 3 Gbps amplitude shift-keying (ASK) signals enables uncompressed high-definition 1080p video delivery. PMID:23736614

  14. Compassion Fade: Affect and Charity Are Greatest for a Single Child in Need

    PubMed Central

    Västfjäll, Daniel; Slovic, Paul; Mayorga, Marcus; Peters, Ellen

    2014-01-01

    Charitable giving in 2013 exceeded $300 billion, but why do we respond to some life-saving causes while ignoring others? In our first two studies, we demonstrated that valuation of lives is associated with affective feelings (self-reported and psychophysiological) and that a decline in compassion may begin with the second endangered life. In Study 3, this fading of compassion was reversed by describing multiple lives in a more unitary fashion. Study 4 extended our findings to loss-frame scenarios. Our capacity to feel sympathy for people in need appears limited, and this form of compassion fatigue can lead to apathy and inaction, consistent with what is seen repeatedly in response to many large-scale human and environmental catastrophes. PMID:24940738

  15. Corrosion/Fragmentation of Layered Composite Cathode and Related Capacity/Voltage Fading during Cycling Process

    SciTech Connect

    Zheng, Jianming; Gu, Meng; Xiao, Jie; Zuo, Pengjian; Wang, Chong M.; Zhang, Jiguang

    2013-06-26

    Pristine and cycled layered structure cathode of Li[Li0.2Ni0.2M0.6]O2 samples are characterized by aberration-corrected scanning transmission electron microscopy and electron energy loss spectroscopy. These analyses provide new insights on capacity/voltage fading mechanism of Li[Li0.2Ni0.2M0.6]O2. Sponge-like structure and fragment pieces were found on the surface of cathode after cycling. Mn2+ species and reduced Li content in the fragments caused significant capacity loss. These results also reveal the functional mechanism of surface coatings, e.g. AlF3, which can protect the electrode from etching by acidic species in the electrolyte, suppress cathode degradation and improve long-term cycling stability.

  16. Modeling the Role of Relationship Fading and Breakup in Social Network Formation.

    PubMed

    Murase, Yohsuke; Jo, Hang-Hyun; Török, János; Kertész, János; Kaski, Kimmo

    2015-01-01

    In social networks of human individuals, social relationships do not necessarily last forever as they can either fade gradually with time, resulting in "link aging," or terminate abruptly, causing "link deletion," as even old friendships may cease. In this paper, we study a social network formation model where we introduce several ways by which a link termination takes place. If we adopt the link aging, we get a more modular structure with more homogeneously distributed link weights within communities than when link deletion is used. By investigating distributions and relations of various network characteristics, we find that the empirical findings are better reproduced with the link deletion model. This indicates that link deletion plays a more prominent role in organizing social networks than link aging. PMID:26176224

  17. Spectral parameter estimation of CAT radar echoes in the presence of fading clutter

    NASA Technical Reports Server (NTRS)

    Sato, T.; Woodman, R. F.

    1980-01-01

    The analysis technique and a part of the results obtained from CAT radar echoes from higher troposphere and lower stratosphere are presented. First, the effect of processing distortion caused by the periodogram method using FFT algorithm on the slowly fading ground clutter echo is discussed. It is shown that an extremely narrow clutter spectrum can spill over the entire frequency range if the data are truncated at a tie sorter than their correlation time affecting largely the estimation of the CAT spectrum contribution, especially when the latter is a few tens of dB weaker than the former. A nonlinear least squares fitting procedure is used to parameterize the observed power spectrum in terms of CAT echo power, Doppler shift, spectral width, and the parameters which specify the shape of the clutter component.

  18. Kinetics of Crystal Violet Fading in the Presence of TX-100, DTAB and SDS.

    PubMed

    Samiey, Babak; Ashoori, Fatemeh

    2011-06-01

    The rate constant of alkaline fading of crystal violet (CV+) was measured in the presence of non ionic (TX-100), cationic (DTAB) and anionic (SDS) surfactants. This reaction was studied at 283-303 K. The rate of reaction showed remarkable dependence on the electrical charge of the used surfactants. It was observed that the reaction rate constant increased in the presence of TX-100 and DTAB and decreased in the presence of SDS. Binding constants of CV+ with TX-100 and DTAB and the related thermodynamic parameters were obtained by classical (or stoichiometric) model. The results show that binding of CV+ to TX-100 is endothermic and binding of CV+ to DTAB and SDS is exothermic in the used concentration range of surfactants.

  19. Swift/XRT monitoring of SN2011dh: evidence for fading

    NASA Astrophysics Data System (ADS)

    Margutti, R.; Soderberg, A.

    2011-06-01

    We have analyzed 24 ks of Swift/XRT data of SN1011dh (Silverman et al. 2001, Atel #3398; Reiland et al. 2011, CBET #2736) collected in the time period June 3-7. In agreement with Campana & Burrows (2011, Atel #3414) we find that the source is detected at an average level of ~6 E-03 c/s. We furthermore find that the source has faded from ~1.3 E-02 c/s to ~3 E-03 c/s, with a power-law decay index of alpha~ -1.8 (+0.6,-0.6 90% c.l.) The probability of a chance fluctuation is below 0.01% (binomial test), thus we conclude that the observed decay is statistically significant.

  20. Modeling the Role of Relationship Fading and Breakup in Social Network Formation

    PubMed Central

    Murase, Yohsuke; Jo, Hang-Hyun; Török, János; Kertész, János; Kaski, Kimmo

    2015-01-01

    In social networks of human individuals, social relationships do not necessarily last forever as they can either fade gradually with time, resulting in “link aging,” or terminate abruptly, causing “link deletion,” as even old friendships may cease. In this paper, we study a social network formation model where we introduce several ways by which a link termination takes place. If we adopt the link aging, we get a more modular structure with more homogeneously distributed link weights within communities than when link deletion is used. By investigating distributions and relations of various network characteristics, we find that the empirical findings are better reproduced with the link deletion model. This indicates that link deletion plays a more prominent role in organizing social networks than link aging. PMID:26176224

  1. Identifying fade mechanisms in high-power lithium-ion cells.

    SciTech Connect

    Abraham, D. P.; Knuth, J.; Dees, D. W.; Jansen, A. N.; Sammann, E.; Haasch, R.; Twesten, R. D.; MacLaren, S.; Chemical Engineering; Univ. of Illinois

    2004-01-01

    Hybrid electric vehicles (HEV) need long-lived high-power batteries as energy storage devices. Batteries based on lithium-ion technology can meet the high-power goals but have been unable to meet HEV calendar-life requirements. As part of the US Department of Energy's Advanced Technology Development (ATD) Program, diagnostic studies are being conducted on 18650-type lithium-ion cells that were subjected to accelerated aging tests at temperatures ranging from 40 to 70 C. This article summarizes data obtained by gas chromatography, liquid chromatography, electron microscopy, X-ray spectroscopy and electrochemical techniques, and identifies cell components that are responsible for the observed impedance rise and power fade.

  2. Slowly fading super-luminous supernovae that are not pair-instability explosions.

    PubMed

    Nicholl, M; Smartt, S J; Jerkstrand, A; Inserra, C; McCrum, M; Kotak, R; Fraser, M; Wright, D; Chen, T-W; Smith, K; Young, D R; Sim, S A; Valenti, S; Howell, D A; Bresolin, F; Kudritzki, R P; Tonry, J L; Huber, M E; Rest, A; Pastorello, A; Tomasella, L; Cappellaro, E; Benetti, S; Mattila, S; Kankare, E; Kangas, T; Leloudas, G; Sollerman, J; Taddia, F; Berger, E; Chornock, R; Narayan, G; Stubbs, C W; Foley, R J; Lunnan, R; Soderberg, A; Sanders, N; Milisavljevic, D; Margutti, R; Kirshner, R P; Elias-Rosa, N; Morales-Garoffolo, A; Taubenberger, S; Botticella, M T; Gezari, S; Urata, Y; Rodney, S; Riess, A G; Scolnic, D; Wood-Vasey, W M; Burgett, W S; Chambers, K; Flewelling, H A; Magnier, E A; Kaiser, N; Metcalfe, N; Morgan, J; Price, P A; Sweeney, W; Waters, C

    2013-10-17

    Super-luminous supernovae that radiate more than 10(44) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of (56)Ni are synthesized; this isotope decays to (56)Fe via (56)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10(-6) times that of the core-collapse rate. PMID:24132291

  3. X-RAY FADING AND EXPANSION IN THE “MINIATURE SUPERNOVA REMNANT” OF GK PERSEI

    SciTech Connect

    Takei, D.; Drake, J. J.; Slane, P.; Yamaguchi, H.; Uchiyama, Y.; Katsuda, S.

    2015-03-10

    We report on a second epoch of Chandra X-ray imaging spectroscopy of the spatially resolved old nova remnant GK Persei. An ACIS-S3 observation of 97.4 ks was conducted in 2013 November after a lapse of 13.8 yr from the last visit in 2000. The X-ray emitting nebula appeared more faint and patchy compared with the first epoch. The flux decline was particularly evident in fainter regions and the mean decline was 30%–40% in the 0.5–1.2 keV energy band. A typical expansion of the brightest part of the remnant was 1.″9, which corresponds to an expansion rate of 0.″14 yr{sup −1}. The soft X-ray spectra extracted from both the 2000 and 2013 data can be explained by a non-equilibrium ionization collisional plasma model convolved with interstellar absorption, though do not allow us to constrain the origin of the flux evolution. The plasma temperature has not significantly evolved since the 2000 epoch and we conclude that the fading of the X-ray emission is due largely to expansion. This implies that recent expansion has been into a lower density medium, a scenario that is qualitatively consistent with the structure of the circumstellar environment photographed soon after the initial explosion more than a century ago. Fainter areas are fading more quickly than brighter areas, indicating that they are fainter because of a lower ambient medium density and consequently more rapid expansion.

  4. Slowly fading super-luminous supernovae that are not pair-instability explosions

    NASA Astrophysics Data System (ADS)

    Nicholl, M.; Smartt, S. J.; Jerkstrand, A.; Inserra, C.; McCrum, M.; Kotak, R.; Fraser, M.; Wright, D.; Chen, T.-W.; Smith, K.; Young, D. R.; Sim, S. A.; Valenti, S.; Howell, D. A.; Bresolin, F.; Kudritzki, R. P.; Tonry, J. L.; Huber, M. E.; Rest, A.; Pastorello, A.; Tomasella, L.; Cappellaro, E.; Benetti, S.; Mattila, S.; Kankare, E.; Kangas, T.; Leloudas, G.; Sollerman, J.; Taddia, F.; Berger, E.; Chornock, R.; Narayan, G.; Stubbs, C. W.; Foley, R. J.; Lunnan, R.; Soderberg, A.; Sanders, N.; Milisavljevic, D.; Margutti, R.; Kirshner, R. P.; Elias-Rosa, N.; Morales-Garoffolo, A.; Taubenberger, S.; Botticella, M. T.; Gezari, S.; Urata, Y.; Rodney, S.; Riess, A. G.; Scolnic, D.; Wood-Vasey, W. M.; Burgett, W. S.; Chambers, K.; Flewelling, H. A.; Magnier, E. A.; Kaiser, N.; Metcalfe, N.; Morgan, J.; Price, P. A.; Sweeney, W.; Waters, C.

    2013-10-01

    Super-luminous supernovae that radiate more than 1044 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of `pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of 56Ni are synthesized; this isotope decays to 56Fe via 56Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10-6 times that of the core-collapse rate.

  5. Slowly fading super-luminous supernovae that are not pair-instability explosions.

    PubMed

    Nicholl, M; Smartt, S J; Jerkstrand, A; Inserra, C; McCrum, M; Kotak, R; Fraser, M; Wright, D; Chen, T-W; Smith, K; Young, D R; Sim, S A; Valenti, S; Howell, D A; Bresolin, F; Kudritzki, R P; Tonry, J L; Huber, M E; Rest, A; Pastorello, A; Tomasella, L; Cappellaro, E; Benetti, S; Mattila, S; Kankare, E; Kangas, T; Leloudas, G; Sollerman, J; Taddia, F; Berger, E; Chornock, R; Narayan, G; Stubbs, C W; Foley, R J; Lunnan, R; Soderberg, A; Sanders, N; Milisavljevic, D; Margutti, R; Kirshner, R P; Elias-Rosa, N; Morales-Garoffolo, A; Taubenberger, S; Botticella, M T; Gezari, S; Urata, Y; Rodney, S; Riess, A G; Scolnic, D; Wood-Vasey, W M; Burgett, W S; Chambers, K; Flewelling, H A; Magnier, E A; Kaiser, N; Metcalfe, N; Morgan, J; Price, P A; Sweeney, W; Waters, C

    2013-10-17

    Super-luminous supernovae that radiate more than 10(44) ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae. Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of (56)Ni are synthesized; this isotope decays to (56)Fe via (56)Co, powering bright light curves. Such massive progenitors are expected to have formed from metal-poor gas in the early Universe. Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova. Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae, which are not powered by radioactivity. Modelling our observations with 10-16 solar masses of magnetar-energized ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 × 10(-6) times that of the core-collapse rate.

  6. Visible Persistence of Single-Transient Random Dot Patterns: Spatial Parameters Affect the Duration of Fading Percepts.

    PubMed

    Bruchmann, Maximilian; Thaler, Kathrin; Vorberg, Dirk

    2015-01-01

    Visible persistence refers to the continuation of visual perception after the physical termination of a stimulus. We studied an extreme case of visible persistence by presenting two matrices of randomly distributed black and white pixels in succession. On the transition from one matrix to the second, the luminance polarity of all pixels within a disk- or annulus-shaped area reversed, physically creating a single second-order transient signal. This transient signal produces the percept of a disk or an annulus with an abrupt onset and a gradual offset. To study the nature of this fading percept we varied spatial parameters, such as the inner and the outer diameter of annuli (Experiment I) and the radius and eccentricity of disks (Experiment III), and measured the duration of visible persistence by having subjects adjust the synchrony of the onset of a reference stimulus with the onset or the offset of the fading percept. We validated this method by comparing two modalities of the reference stimuli (Experiment I) and by comparing the judgments of fading percepts with the judgments of stimuli that actually fade in luminance contrast (Experiment II). The results show that (i) irrespective of the reference modality, participants are able to precisely judge the on- and the offsets of the fading percepts, (ii) auditory reference stimuli lead to higher visible persistence durations than visual ones, (iii) visible persistence duration increases with the thickness of annuli and the diameter of disks, but decreases with the diameter of annuli, irrespective of stimulus eccentricity. These effects cannot be explained by stimulus energy, which suggests that more complex processing mechanisms are involved. Seemingly contradictory effects of disk and annulus diameter can be unified by assuming an abstract filling-in mechanism that speeds up with the strength of the edge signal and takes more time the larger the stimulus area is.

  7. Channel characterization in high-speed railway station environments at 1.89 GHz

    NASA Astrophysics Data System (ADS)

    Zhou, Tao; Tao, Cheng; Salous, Sana; Liu, Liu; Tan, Zhenhui

    2015-11-01

    Channel characterization is the prerequisite condition for the research and development of the next-generation high-speed railway (HSR) communication system. Train station is one of typical HSR scenarios, where channel characteristics have not yet been investigated sufficiently. In this paper, wideband multiantenna channel measurements are performed at 1.89 GHz in an open-type train station environment based on long-term evolution networks along Beijing to Tianjin HSR in China. Large-scale characteristics of the HSR station channel, focusing on path loss, shadow fading (SF), and the autocorrelation property of SF, are studied. Moreover, small-scale characteristics, such as Ricean K-factor, delay spread, and spatial correlation, are analyzed and modeled. In addition, the stationary region is characterized using the RUN test method. The obtained results provide useful information for deployment and assessment of the future HSR communication system in the HSR station scenario.

  8. Doppler-shift estimation of flat underwater channel using data-aided least-square approach

    NASA Astrophysics Data System (ADS)

    Pan, Weiqiang; Liu, Ping; Chen, Fangjiong; Ji, Fei; Feng, Jing

    2015-06-01

    In this paper we proposed a dada-aided Doppler estimation method for underwater acoustic communication. The training sequence is non-dedicate, hence it can be designed for Doppler estimation as well as channel equalization. We assume the channel has been equalized and consider only flat-fading channel. First, based on the training symbols the theoretical received sequence is composed. Next the least square principle is applied to build the objective function, which minimizes the error between the composed and the actual received signal. Then an iterative approach is applied to solve the least square problem. The proposed approach involves an outer loop and inner loop, which resolve the channel gain and Doppler coefficient, respectively. The theoretical performance bound, i.e. the Cramer-Rao Lower Bound (CRLB) of estimation is also derived. Computer simulations results show that the proposed algorithm achieves the CRLB in medium to high SNR cases.

  9. Equalization in redundant channels

    NASA Technical Reports Server (NTRS)

    Tulpule, Bhalchandra R. (Inventor); Collins, Robert E. (Inventor); Cominelli, Donald F. (Inventor); O'Neill, Richard D. (Inventor)

    1988-01-01

    A miscomparison between a channel's configuration data base and a voted system configuration data base in a redundant channel system having identically operating, frame synchronous channels triggers autoequalization of the channel's historical signal data bases in a hierarchical, chronological manner with that of a correctly operating channel. After equalization, symmetrization of the channel's configuration data base with that of the system permits upgrading of the previously degraded channel to full redundancy. An externally provided equalization command, e.g., manually actuated, can also trigger equalization.

  10. Mn(II) deposition on anodes and its effects on capacity fade in spinel lithium manganate-carbon systems.

    PubMed

    Zhan, Chun; Lu, Jun; Jeremy Kropf, A; Wu, Tianpin; Jansen, Andrew N; Sun, Yang-Kook; Qiu, Xinping; Amine, Khalil

    2013-01-01

    Dissolution and migration of manganese from cathode lead to severe capacity fading of lithium manganate-carbon cells. Overcoming this major problem requires a better understanding of the mechanisms of manganese dissolution, migration and deposition. Here we apply a variety of advanced analytical methods to study lithium manganate cathodes that are cycled with different anodes. We show that the oxidation state of manganese deposited on the anodes is +2, which differs from the results reported earlier. Our results also indicate that a metathesis reaction between Mn(II) and some species on the solid-electrolyte interphase takes place during the deposition of Mn(II) on the anodes, rather than a reduction reaction that leads to the formation of metallic Mn, as speculated in earlier studies. The concentration of Mn deposited on the anode gradually increases with cycles; this trend is well correlated with the anodes rising impedance and capacity fading of the cell.

  11. A Comparison of the Effects of Two Prompt-Fading Strategies on Skill Acquisition in Children with Autism Spectrum Disorders.

    PubMed

    Cengher, Mirela; Shamoun, Kimberly; Moss, Patricia; Roll, David; Feliciano, Gina; Fienup, Daniel M

    2016-06-01

    Research has demonstrated that most-to-least (MTL) and least-to-most (LTM) prompting are effective in helping children with Autism Spectrum Disorders acquire a variety of new skills. However, when directly compared to one another, the efficiency and efficacy of the prompting procedures have been variable. The inconsistencies in the literature could be due to selecting prompt topographies that do not promote correct responding. To address this, the present study began by assessing different prompt topographies and then compared most-to-least (MTL) and least-to-most (LTM) prompt-fading with only prompt topographies that were potent enough to promote correct responding. The subsequent comparison of prompt-fading procedures revealed that MTL prompting was more effective and efficient than LTM prompting for all three participants. Further implications for practice and future research are discussed. PMID:27606243

  12. A fading-based method for checking the presence of closely overlapping peaks in thermoluminescent (TL) materials

    NASA Astrophysics Data System (ADS)

    Furetta, C.

    The paper describes a method, based on fading experiment, for determining the presence of a complex structure in the thermoluminescent glow curve emission from herbs, e.g. oregano and nopal. Because of the polymineral content of the inorganic part of these herbs, the emitted glow curve is the result of several overlapping glow peaks, each one corresponding to another mineral. The initial rise method is also used for determining the activation energy of each component.

  13. Channel nut tool

    DOEpatents

    Olson, Marvin

    2016-01-12

    A method, system, and apparatus for installing channel nuts includes a shank, a handle formed on a first end of a shank, and an end piece with a threaded shaft configured to receive a channel nut formed on the second end of the shaft. The tool can be used to insert or remove a channel nut in a channel framing system and then removed from the channel nut.

  14. Age of Martian channels

    NASA Technical Reports Server (NTRS)

    Malin, M. C.

    1976-01-01

    The ages of large Martian channels have been studied by determining the relative abundances of craters superimposed on channels and adjacent terrains and by examining superposition relationships between channels and plains and mantle materials. The channels are extremely old, are spatially confined and temporally related to the ancient cratered terrain, and in many cases are related to the as yet poorly understood genetic processes of fretting and chaos formation. No evidence is found for recent channel activity.

  15. The fading behavior of the propagating VLF signal during the recovery time of solar flares.

    NASA Astrophysics Data System (ADS)

    Bouderba, Yasmina; Tribeche, Mouloud; Nait Amor, Samir

    2016-07-01

    The VLF radio signal propagating in the waveguide delimited by the Earth's surface and the D-layer of the ionosphere undergoes important modifications due to solar flares. In this work we focus on the NRK (37.5 kHz) VLF transmitter signal that propagates along the medium path to Algiers receiver (distance=3495 km). The signal analysis of two different flare classes shows that the perturbation due to a week flare of C2.1 (I _{max}=2.1 x 10 ^{-6} W/m ^{2}) class are less important than the medium one of M3.2 (I _{max}=3.2 x 10 ^{-5} W/m ^{2}) class. This leads to the fast recovery to the normal ionospheric condition after the weak solar flare while the medium solar flare takes more time. Additionally, the study of the signal amplitude behaviors by means of the LWPC code shows that the fading displacement toward the transmitter is more significant in the case of M3.2 flare than C2.1 class.

  16. Beneficial Effects of Ischemic Preconditioning in Resistance Exercise Fade Over Time.

    PubMed

    Marocolo, M; Marocolo, I C; da Mota, G R; Simão, R; Maior, A S; Coriolano, H-J Appell

    2016-09-01

    This study evaluated the effect of ischemic preconditioning (IPC) on resistance exercise performance in upper limbs. After 12-RM load determination, 21 men attended 4 trials separated by 3 days in a randomized crossover design: IPC (4×5-min occlusion 220 mmHg/reperfusion 0 mmHg) in arms and in thighs, and SHAM (equal to the IPC protocol but "occlusion" at 20 mmHg) in arms and in thighs. 8 min following the respective interventions, the subjects performed one set of resistance exercise in elbow flexion with the 12-RM load until concentric failure. The number of repetitions increased for both protocols in arm (IPC=14.1±2.5 and SHAM=14.4±3.0) and in thigh (IPC=14.3±2.2 and SHAM=13.4±1.7). However, the number of repetitions tended to decrease over the 4 trials and no more effect was found in the fourth trial. Therefore, IPC or SHAM may enhance performance in resistance exercise for upper limbs, but this effect apparently fades over time.

  17. Autonomous Information Fading and Provision to Achieve High Response Time in Distributed Information Systems

    NASA Astrophysics Data System (ADS)

    Lu, Xiaodong; Arfaoui, Helene; Mori, Kinji

    In highly dynamic electronic commerce environment, the need for adaptability and rapid response time to information service systems has become increasingly important. In order to cope with the continuously changing conditions of service provision and utilization, Faded Information Field (FIF) has been proposed. FIF is a distributed information service system architecture, sustained by push/pull mobile agents to bring high-assurance of services through a recursive demand-oriented provision of the most popular information closer to the users to make a tradeoff between the cost of information service allocation and access. In this paper, based on the analysis of the relationship that exists among the users distribution, information provision and access time, we propose the technology for FIF design to resolve the competing requirements of users and providers to improve users' access time. In addition, to achieve dynamic load balancing with changing users preference, the autonomous information reallocation technology is proposed. We proved the effectiveness of the proposed technology through the simulation and comparison with the conventional system.

  18. A DOUBLE NEUTRON STAR MERGER ORIGIN FOR THE COSMOLOGICAL RELATIVISTIC FADING SOURCE PTF11agg?

    SciTech Connect

    Wu, Xue-Feng; Gao, He; Ding, Xuan; Zhang, Bing; Dai, Zi-Gao; Wei, Jian-Yan

    2014-01-20

    The Palomar Transient Factory (PTF) team recently reported the discovery of a rapidly fading optical transient source, PTF11agg. A long-lived scintillating radio counterpart was identified, but the search for a high-energy counterpart showed negative results. The PTF team speculated that PTF11agg may represent a new class of relativistic outbursts. Here we suggest that a neutron star (NS)-NS merger system with a supra-massive magnetar central engine could be a possible source to power such a transient, if our line of sight is not on the jet axis direction of the system. These systems are also top candidates for gravitational wave sources to be detected in the advanced LIGO/Virgo era. We find that the PTF11agg data could be explained well with such a model, suggesting that at least some gravitational wave bursts due to NS-NS mergers may be associated with such a bright electromagnetic counterpart without a γ-ray trigger.

  19. Wideband signal detection using a Nyquist folding analog-to-information receiver in multipath fading environment

    NASA Astrophysics Data System (ADS)

    Odejide, Olusegun; Annamalai, Annamalai; Akujuobi, Cajetan

    2010-04-01

    The need to efficiently and effectively monitor the frequency spectrum for identification of unoccupied bands is essential in communication systems such as Cognitive Radio (CR), battlefield communications, etc. The Nyquist Folding Analog-to-Information Receiver (NYFR) which is based on the theory of Compressed Sensing has been proposed recently to address this problem in a sparse environment. Although, typical CS techniques, involve random projections followed by a computationally intensive signal reconstruction process, the methods used in NYFR does not requires the laborious l1 minimization algorithm. The NYFR performs analog compression via a non-uniform sampling process that induces a chirp-like modulation on each received signal. Signal parameters can simply be determined by using timefrequency analysis techniques without full signal reconstruction. This paper revisits the detection problem of using NYFR for information recovery for appropriate frequency detection when the original signal in the presence of both the additive white Gaussian noise and Rice multipath fading. An automatic detection algorithm was also developed to determine the detected frequency parameters without looking at the FFT spectrogram plot.

  20. Fading Coronal Structure and the Onset of Turbulence in the Young Solar Wind

    NASA Astrophysics Data System (ADS)

    DeForest, C. E.; Matthaeus, W. H.; Viall, N. M.; Cranmer, S. R.

    2016-09-01

    Above the top of the solar corona, the young, slow solar wind transitions from low-β, magnetically structured flow dominated by radial structures to high-β, less structured flow dominated by hydrodynamics. This transition, long inferred via theory, is readily apparent in the sky region close to 10° from the Sun in processed, background-subtracted solar wind images. We present image sequences collected by the inner Heliospheric Imager instrument on board the Solar-Terrestrial Relations Observatory (STEREO/HI1) in 2008 December, covering apparent distances from approximately 4° to 24° from the center of the Sun and spanning this transition in the large-scale morphology of the wind. We describe the observation and novel techniques to extract evolving image structure from the images, and we use those data and techniques to present and quantify the clear textural shift in the apparent structure of the corona and solar wind in this altitude range. We demonstrate that the change in apparent texture is due both to anomalous fading of the radial striae that characterize the corona and to anomalous relative brightening of locally dense puffs of solar wind that we term “flocculae.” We show that these phenomena are inconsistent with smooth radial flow, but consistent with the onset of hydrodynamic or magnetohydrodynamic instabilities leading to a turbulent cascade in the young solar wind.

  1. Light-induced fading of the PSL signal from irradiated herbs and spices

    NASA Astrophysics Data System (ADS)

    Alberti, A.; Corda, U.; Fuochi, P.; Bortolin, E.; Calicchia, A.; Onori, S.

    2007-08-01

    Reliability of the photo-stimulated luminescence (PSL) technique, as screening method for irradiated food identification, has been tested with three kinds of herbs and spices (oregano, red pepper and fennel), prepared in two different ways (granular: i.e. seeds and flakes, or powdered), over a long period of storage with different light exposures. The irradiated samples kept in the dark gave always a positive response (the sample is correctly classified as "irradiated") for the overall examination period. The samples kept under ambient light conditions, in typical commercial glass containers, exhibited a reduction of the PSL signal, more or less pronounced depending on the type of food and packaging. The different PSL response of the irradiated samples is to be related to the quantity and quality of the mineral debris present in the individual food. It was also found that, for the same type of food, the light-induced fading was much stronger for the flaked and seed samples than for the corresponding powder samples, the penetrating capability of light being much more inhibited in powdered than in whole seeds or flaked form samples. The observed light bleaching of the PSL signal in irradiated herbs and spices is of practical relevance since it may lead to false negative classifications.

  2. MIMO free-space optical communication employing coherent BPOLSK modulation in atmospheric optical turbulence channel with pointing errors

    NASA Astrophysics Data System (ADS)

    Prabu, K.; Kumar, D. Sriram

    2015-05-01

    An optical wireless communication system is an alternative to radio frequency communication, but atmospheric turbulence induced fading and misalignment fading are the main impairments affecting an optical signal when propagating through the turbulence channel. The resultant of misalignment fading is the pointing errors, it degrades the bit error rate (BER) performance of the free space optics (FSO) system. In this paper, we study the BER performance of the multiple-input multiple-output (MIMO) FSO system employing coherent binary polarization shift keying (BPOLSK) in gamma-gamma (G-G) channel with pointing errors. The BER performance of the BPOLSK based MIMO FSO system is compared with the single-input single-output (SISO) system. Also, the average BER performance of the systems is analyzed and compared with and without pointing errors. A novel closed form expressions of BER are derived for MIMO FSO system with maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques. The analytical results show that the pointing errors can severely degrade the performance of the system.

  3. LED fluorescence microscopy in the diagnosis of tuberculosis: Fading and restaining of smears for external quality assessment.

    PubMed

    Allassia, Sonia; Aranibar, Mónica; Boutonnet, Mónica; Caserío, Viviana; Etchart, Ana Alicia; Fajardo, Sandra; García, Mónica; Gomez, Noemí; Gunia, Alba Marisa; Gustincic, María Virginia; Izquierdo, Viviana; Jara, Arnaldo Andrés; Kozicky, Graciela; Matteo, Mario; Pellegrini, Carlos; Pellegrino, Silvia; Pérez Catalán, Sebastián; Poggi, Susana; Sacramone, Carina; Santiso, Gabriela María; Souto, Alejandro; Togneri, Ana María; Wolff, Lidia; Vilche, Sandra; Eletti, Daniel; Imaz, María Susana

    2016-01-01

    Blinded rechecking is a method proposed for external quality assurance (EQA) of auramine-stained acid-fast bacilli (AFB) smears using fluorescence microscopy (FM), however, this procedure is not well developed and slides fading over time could compromise its implementation. Since bleaching of fluorescent molecules involves temperature-dependent chemical reactions, it is likely that low temperatures could slow down this process. We stored auramine-stained slides under different environmental conditions, including -20°C, and examined them over time. The slides stored in all the environments faded. At -20°C, fading was not reduced in relation to room temperature. Restaining and re-examining smears after five months showed that the slides containing saliva and storage at -20°C were associated with failure in AFB reappearance. In conclusion, the practice of freezing slides until they are viewed should be discouraged as it has a negative effect on blinded rechecking by reducing reading concordance after restaining. Specimen quality should be considered when interpreting FM-EQA results. PMID:27291283

  4. LED fluorescence microscopy in the diagnosis of tuberculosis: Fading and restaining of smears for external quality assessment.

    PubMed

    Allassia, Sonia; Aranibar, Mónica; Boutonnet, Mónica; Caserío, Viviana; Etchart, Ana Alicia; Fajardo, Sandra; García, Mónica; Gomez, Noemí; Gunia, Alba Marisa; Gustincic, María Virginia; Izquierdo, Viviana; Jara, Arnaldo Andrés; Kozicky, Graciela; Matteo, Mario; Pellegrini, Carlos; Pellegrino, Silvia; Pérez Catalán, Sebastián; Poggi, Susana; Sacramone, Carina; Santiso, Gabriela María; Souto, Alejandro; Togneri, Ana María; Wolff, Lidia; Vilche, Sandra; Eletti, Daniel; Imaz, María Susana

    2016-01-01

    Blinded rechecking is a method proposed for external quality assurance (EQA) of auramine-stained acid-fast bacilli (AFB) smears using fluorescence microscopy (FM), however, this procedure is not well developed and slides fading over time could compromise its implementation. Since bleaching of fluorescent molecules involves temperature-dependent chemical reactions, it is likely that low temperatures could slow down this process. We stored auramine-stained slides under different environmental conditions, including -20°C, and examined them over time. The slides stored in all the environments faded. At -20°C, fading was not reduced in relation to room temperature. Restaining and re-examining smears after five months showed that the slides containing saliva and storage at -20°C were associated with failure in AFB reappearance. In conclusion, the practice of freezing slides until they are viewed should be discouraged as it has a negative effect on blinded rechecking by reducing reading concordance after restaining. Specimen quality should be considered when interpreting FM-EQA results.

  5. Simulation of the fading of photographic three-color materials: a new tool for the preservation field

    NASA Astrophysics Data System (ADS)

    Frey, Franziska S.; Gschwind, Rudolf; Reilly, James M.

    1995-04-01

    Photography and motion pictures play an important role in our society as information carriers, artistic medium, and historical document, representing cultural values which have to be preserved. The emerging electronic imaging techniques help in developing new methods to accomplish this goal. The dyes of common photographic three-color materials are chemically rather unstable. Both the thermodynamic and the photochemical stability is low. As a result, millions of photographs and thousands of films deteriorate, if not preserved and stored under optimal conditions. It is of great interest to curators of museums that house photographic or cinematographic collections to simulate and visualize the fading process. A multimedia production including images and further information offers a direct and convincing way to demonstrate the different effects of various storage alternatives on dye loss. This project is an example of an interdisciplinary approach that includes photography, conservation, and computer science. The simulation program used for the creation of the faded images is based on algorithms developed for the reconstruction of faded color photographic materials.

  6. Multi-carrier Communications over Time-varying Acoustic Channels

    NASA Astrophysics Data System (ADS)

    Aval, Yashar M.

    Acoustic communication is an enabling technology for many autonomous undersea systems, such as those used for ocean monitoring, offshore oil and gas industry, aquaculture, or port security. There are three main challenges in achieving reliable high-rate underwater communication: the bandwidth of acoustic channels is extremely limited, the propagation delays are long, and the Doppler distortions are more pronounced than those found in wireless radio channels. In this dissertation we focus on assessing the fundamental limitations of acoustic communication, and designing efficient signal processing methods that cam overcome these limitations. We address the fundamental question of acoustic channel capacity (achievable rate) for single-input-multi-output (SIMO) acoustic channels using a per-path Rician fading model, and focusing on two scenarios: narrowband channels where the channel statistics can be approximated as frequency- independent, and wideband channels where the nominal path loss is frequency-dependent. In each scenario, we compare several candidate power allocation techniques, and show that assigning uniform power across all frequencies for the first scenario, and assigning uniform power across a selected frequency-band for the second scenario, are the best practical choices in most cases, because the long propagation delay renders the feedback information outdated for power allocation based on the estimated channel response. We quantify our results using the channel information extracted form the 2010 Mobile Acoustic Communications Experiment (MACE'10). Next, we focus on achieving reliable high-rate communication over underwater acoustic channels. Specifically, we investigate orthogonal frequency division multiplexing (OFDM) as the state-of-the-art technique for dealing with frequency-selective multipath channels, and propose a class of methods that compensate for the time-variation of the underwater acoustic channel. These methods are based on multiple

  7. Sensing propagation events and fade statistics at C-band for two over-water, line-of-sight propagation paths over a one year period

    NASA Technical Reports Server (NTRS)

    Goldhirsh, Julius; Dockery, G. Daniel; Musiani, Bert H.

    1992-01-01

    We examine signal fading statistics over a year period corresponding to two over-water, line-of-site, propagation links in the mid-Atlantic coast of the US. These links are comprised of a transmitter on a tower at Parramore Island, VA operating at 4.7 GHz sending simultaneous cw signals to two receiver systems located on a lighthouse and a lookout tower on Assateague Beach, VA at distances of 44 and 39 km, respectively. The receiving sites are separated by approximately 5 km. Cumulative fade distributions corresponding to yearly, monthly, and diurnal time scales were derived. Fade duration statistics correspond to sustained attenuation events were also derived. These events, which were arbitrarily defined as having fades relative to free space powers in excess of 20 dB for durations of two hours or more, are believed to be generally due to subrefraction. Analysis of synoptic weather conditions and nearby rawindsonde data during two sustained deep fading periods showed atmospheric conditions consistent with extreme subrefraction, where the refractivity-height profile had a positive lapse rate. The efficacy of employing the links as indicators of real time conditions of atmospheric propagation was also demonstrated by a telephone call-up procedure which enabled displays of time series of the fading at remote locations to be generated.

  8. Effects of source spatial partial coherence on temporal fade statistics of irradiance flux in free-space optical links through atmospheric turbulence.

    PubMed

    Chen, Chunyi; Yang, Huamin; Zhou, Zhou; Zhang, Weizhi; Kavehrad, Mohsen; Tong, Shoufeng; Wang, Tianshu

    2013-12-01

    The temporal covariance function of irradiance-flux fluctua-tions for Gaussian Schell-model (GSM) beams propagating in atmospheric turbulence is theoretically formulated by making use of the method of effective beam parameters. Based on this formulation, new expressions for the root-mean-square (RMS) bandwidth of the irradiance-flux temporal spectrum due to GSM beams passing through atmospheric turbulence are derived. With the help of these expressions, the temporal fade statistics of the irradiance flux in free-space optical (FSO) communication systems, using spatially partially coherent sources, impaired by atmospheric turbulence are further calculated. Results show that with a given receiver aperture size, the use of a spatially partially coherent source can reduce both the fractional fade time and average fade duration of the received light signal; however, when atmospheric turbulence grows strong, the reduction in the fractional fade time becomes insignificant for both large and small receiver apertures and in the average fade duration turns inconsiderable for small receiver apertures. It is also illustrated that if the receiver aperture size is fixed, changing the transverse correlation length of the source from a larger value to a smaller one can reduce the average fade frequency of the received light signal only when a threshold parameter in decibels greater than the critical threshold level is specified.

  9. Channel correlation of transmit diversity FSO systems with partially coherent optical beams

    NASA Astrophysics Data System (ADS)

    Wang, Xiaoyang; Yao, Mingwu; Yi, Xiang; Liu, Zengji; Qiu, Zhiliang

    2015-01-01

    Spatial diversity, including transmit diversity, has been proven to be a promising technique to mitigate turbulence-induced signal fading. However, due to the limitation of size in compact FSO (free-space optical) terminals, the transmit antennas cannot always be separated far enough from each other, resulting in increased channel correlation and deteriorated diversity performance. In this paper, we focus on the channel correlation statistics of transmit diversity FSO systems with two transmit beams. Specifically, we consider partially coherent optical beams, which reduce scintillation over fully coherent optical beams. We perform theoretical analysis and obtain some interesting numerical results, such as the degree of channel correlation which changed mainly with source correlation radius from 0.001 to 0.1 m. These results can be helpful for designing transmit diversity FSO systems with partially coherent beams.

  10. Microfluidic channel fabrication method

    DOEpatents

    Arnold, Don W.; Schoeniger, Joseph S.; Cardinale, Gregory F.

    2001-01-01

    A new channel structure for microfluidic systems and process for fabricating this structure. In contrast to the conventional practice of fabricating fluid channels as trenches or grooves in a substrate, fluid channels are fabricated as thin walled raised structures on a substrate. Microfluidic devices produced in accordance with the invention are a hybrid assembly generally consisting of three layers: 1) a substrate that can or cannot be an electrical insulator; 2) a middle layer, that is an electrically conducting material and preferably silicon, forms the channel walls whose height defines the channel height, joined to and extending from the substrate; and 3) a top layer, joined to the top of the channels, that forms a cover for the channels. The channels can be defined by photolithographic techniques and are produced by etching away the material around the channel walls.

  11. Performance analysis of a finite radon transform in OFDM system under different channel models

    SciTech Connect

    Dawood, Sameer A.; Anuar, M. S.; Fayadh, Rashid A.; Malek, F.; Abdullah, Farrah Salwani

    2015-05-15

    In this paper, a class of discrete Radon transforms namely Finite Radon Transform (FRAT) was proposed as a modulation technique in the realization of Orthogonal Frequency Division Multiplexing (OFDM). The proposed FRAT operates as a data mapper in the OFDM transceiver instead of the conventional phase shift mapping and quadrature amplitude mapping that are usually used with the standard OFDM based on Fast Fourier Transform (FFT), by the way that ensure increasing the orthogonality of the system. The Fourier domain approach was found here to be the more suitable way for obtaining the forward and inverse FRAT. This structure resulted in a more suitable realization of conventional FFT- OFDM. It was shown that this application increases the orthogonality significantly in this case due to the use of Inverse Fast Fourier Transform (IFFT) twice, namely, in the data mapping and in the sub-carrier modulation also due to the use of an efficient algorithm in determining the FRAT coefficients called the optimal ordering method. The proposed approach was tested and compared with conventional OFDM, for additive white Gaussian noise (AWGN) channel, flat fading channel, and multi-path frequency selective fading channel. The obtained results showed that the proposed system has improved the bit error rate (BER) performance by reducing inter-symbol interference (ISI) and inter-carrier interference (ICI), comparing with conventional OFDM system.

  12. Gramicidin Channels: Versatile Tools

    NASA Astrophysics Data System (ADS)

    Andersen, Olaf S.; Koeppe, Roger E., II; Roux, Benoît

    Gramicidin channels are miniproteins in which two tryptophan-rich subunits associate by means of transbilayer dimerization to form the conducting channels. That is, in contrast to other ion channels, gramicidin channels do not open and close; they appear and disappear. Each subunit in the bilayer-spanning channel is tied to the bilayer/solution interface through hydrogen bonds that involve the indole NH groups as donors andwater or the phospholipid backbone as acceptors. The channel's permeability characteristics are well-defined: gramicidin channels are selective for monovalent cations, with no measurable permeability to anions or polyvalent cations; ions and water move through a pore whose wall is formed by the peptide backbone; and the single-channel conductance and cation selectivity vary when the amino acid sequence is varied, even though the permeating ions make no contact with the amino acid side chains. Given the plethora of available experimental information—for not only the wild-type channels but also for channels formed by amino acid-substituted gramicidin analogues—gramicidin channels continue to provide important insights into the microphysics of ion permeation through bilayer-spanning channels. For similar reasons, gramicidin channels constitute a system of choice for evaluating computational strategies for obtaining mechanistic insights into ion permeation through the more complex channels formed by integral membrane proteins.

  13. Evolution of l-photon excited thermo vacuum state in a single-mode damping channel

    NASA Astrophysics Data System (ADS)

    He, Rui; Fan, Hong-Yi

    2016-01-01

    In this paper, we investigate how a kind of non-Gaussian states (l-photon excited thermo vacuum state Cla†l|0(β)>) evolves in a single-mode damping channel. We find that it evolves into a Laguerre-polynomial-weighted real-fictitious squeezed thermo vacuum state, which exhibits strong decoherence and its original nonclassicality fades. In particular, when l = 0, in this damping process the thermo squeezing effect decreases while the fictitious-mode vacuum becomes chaotic. In overcoming the difficulty of calculation, we employ the summation method within ordered product of operators, a new generating function formula about two-variable Hermite polynomials is derived.

  14. Free-space optical channel estimation for physical layer security.

    PubMed

    Endo, Hiroyuki; Fujiwara, Mikio; Kitamura, Mitsuo; Ito, Toshiyuki; Toyoshima, Morio; Takayama, Yoshihisa; Takenaka, Hideki; Shimizu, Ryosuke; Laurenti, Nicola; Vallone, Giuseppe; Villoresi, Paolo; Aoki, Takao; Sasaki, Masahide

    2016-04-18

    We present experimental data on message transmission in a free-space optical (FSO) link at an eye-safe wavelength, using a testbed consisting of one sender and two receiver terminals, where the latter two are a legitimate receiver and an eavesdropper. The testbed allows us to emulate a typical scenario of physical-layer (PHY) security such as satellite-to-ground laser communications. We estimate information-theoretic metrics including secrecy rate, secrecy outage probability, and expected code lengths for given secrecy criteria based on observed channel statistics. We then discuss operation principles of secure message transmission under realistic fading conditions, and provide a guideline on a multi-layer security architecture by combining PHY security and upper-layer (algorithmic) security. PMID:27137325

  15. Free-space optical channel estimation for physical layer security

    NASA Astrophysics Data System (ADS)

    Endo, Hiroyuki; Fujiwara, Mikio; Kitamura, Mitsuo; Ito, Toshiyuki; Toyoshima, Morio; Takayama, Yoshihisa; Takenaka, Hideki; Shimizu, Ryosuke; Laurenti, Nicola; Vallone, Giuseppe; Villoresi, Paolo; Aoki, Takao; Sasaki, Masahide

    2016-04-01

    We present experimental data on message transmission in a free-space optical (FSO) link at an eye-safe wavelength, using a testbed consisting of one sender and two receiver terminals, where the latter two are a legitimate receiver and an eavesdropper. The testbed allows us to emulate a typical scenario of physical-layer (PHY) security such as satellite-to-ground laser communications. We estimate information-theoretic metrics including secrecy rate, secrecy outage probability, and expected code lengths for given secrecy criteria based on observed channel statistics. We then discuss operation principles of secure message transmission under realistic fading conditions, and provide a guideline on a multi-layer security architecture by combining PHY security and upper-layer (algorithmic) security.

  16. Channel Measurement and Modeling for 5G Urban Microcellular Scenarios.

    PubMed

    Peter, Michael; Weiler, Richard J; Göktepe, Barış; Keusgen, Wilhelm; Sakaguchi, Kei

    2016-08-20

    In order to support the development of channel models for higher frequency bands, multiple urban microcellular measurement campaigns have been carried out in Berlin, Germany, at 60 and 10 GHz. In this paper, the collected data is uniformly analyzed with focus on the path loss (PL) and the delay spread (DS). It reveals that the ground reflection has a dominant impact on the fading behavior. For line-of-sight conditions, the PL exponents are close to free space propagation at 60 GHz, but slightly smaller (1.62) for the street canyon at 10 GHz. The DS shows a clear dependence on the scenario (median values between 16 and 38 ns) and a strong distance dependence for the open square and the wide street canyon. The dependence is less distinct for the narrow street canyon with residential buildings. This behavior is consistent with complementary ray tracing simulations, though the simplified model tends to overestimate the DS.

  17. Free-space optical channel estimation for physical layer security.

    PubMed

    Endo, Hiroyuki; Fujiwara, Mikio; Kitamura, Mitsuo; Ito, Toshiyuki; Toyoshima, Morio; Takayama, Yoshihisa; Takenaka, Hideki; Shimizu, Ryosuke; Laurenti, Nicola; Vallone, Giuseppe; Villoresi, Paolo; Aoki, Takao; Sasaki, Masahide

    2016-04-18

    We present experimental data on message transmission in a free-space optical (FSO) link at an eye-safe wavelength, using a testbed consisting of one sender and two receiver terminals, where the latter two are a legitimate receiver and an eavesdropper. The testbed allows us to emulate a typical scenario of physical-layer (PHY) security such as satellite-to-ground laser communications. We estimate information-theoretic metrics including secrecy rate, secrecy outage probability, and expected code lengths for given secrecy criteria based on observed channel statistics. We then discuss operation principles of secure message transmission under realistic fading conditions, and provide a guideline on a multi-layer security architecture by combining PHY security and upper-layer (algorithmic) security.

  18. Channel Measurement and Modeling for 5G Urban Microcellular Scenarios.

    PubMed

    Peter, Michael; Weiler, Richard J; Göktepe, Barış; Keusgen, Wilhelm; Sakaguchi, Kei

    2016-01-01

    In order to support the development of channel models for higher frequency bands, multiple urban microcellular measurement campaigns have been carried out in Berlin, Germany, at 60 and 10 GHz. In this paper, the collected data is uniformly analyzed with focus on the path loss (PL) and the delay spread (DS). It reveals that the ground reflection has a dominant impact on the fading behavior. For line-of-sight conditions, the PL exponents are close to free space propagation at 60 GHz, but slightly smaller (1.62) for the street canyon at 10 GHz. The DS shows a clear dependence on the scenario (median values between 16 and 38 ns) and a strong distance dependence for the open square and the wide street canyon. The dependence is less distinct for the narrow street canyon with residential buildings. This behavior is consistent with complementary ray tracing simulations, though the simplified model tends to overestimate the DS. PMID:27556462

  19. Channel Measurement and Modeling for 5G Urban Microcellular Scenarios

    PubMed Central

    Peter, Michael; Weiler, Richard J.; Göktepe, Barış; Keusgen, Wilhelm; Sakaguchi, Kei

    2016-01-01

    In order to support the development of channel models for higher frequency bands, multiple urban microcellular measurement campaigns have been carried out in Berlin, Germany, at 60 and 10 GHz. In this paper, the collected data is uniformly analyzed with focus on the path loss (PL) and the delay spread (DS). It reveals that the ground reflection has a dominant impact on the fading behavior. For line-of-sight conditions, the PL exponents are close to free space propagation at 60 GHz, but slightly smaller (1.62) for the street canyon at 10 GHz. The DS shows a clear dependence on the scenario (median values between 16 and 38 ns) and a strong distance dependence for the open square and the wide street canyon. The dependence is less distinct for the narrow street canyon with residential buildings. This behavior is consistent with complementary ray tracing simulations, though the simplified model tends to overestimate the DS. PMID:27556462

  20. Cholesterol and Ion Channels

    PubMed Central

    Levitan, Irena; Fang, Yun; Rosenhouse-Dantsker, Avia; Romanenko, Victor

    2010-01-01

    A variety of ion channels, including members of all major ion channel families, have been shown to be regulated by changes in the level of membrane cholesterol and partition into cholesterol-rich membrane domains. In general, several types of cholesterol effects have been described. The most common effect is suppression of channel activity by an increase in membrane cholesterol, an effect that was described for several types of inwardly-rectifying K+ channels, voltage-gated K+ channels, Ca+2 sensitive K+ channels, voltage-gated Na+ channels, N-type voltage-gated Ca+2 channels and volume-regulated anion channels. In contrast, several types of ion channels, such as epithelial amiloride-sensitive Na+ channels and Transient Receptor Potential channels, as well as some of the types of inwardly-rectifying and voltage-gated K+ channels were shown to be inhibited by cholesterol depletion. Cholesterol was also shown to alter the kinetic properties and current-voltage dependence of several voltage-gated channels. Finally, maintaining membrane cholesterol level is required for coupling ion channels to signalling cascades. In terms of the mechanisms, three general mechanisms have been proposed: (i) specific interactions between cholesterol and the channel protein, (ii) changes in the physical properties of the membrane bilayer and (iii) maintaining the scaffolds for protein-protein interactions. The goal of this review is to describe systematically the role of cholesterol in regulation of the major types of ion channels and to discuss these effects in the context of the models proposed. PMID:20213557

  1. Ecology and behavior of the Midget Faded Rattlesnake (Crotalus oreganus concolor) in Wyoming

    USGS Publications Warehouse

    Parker, J.M.; Anderson, S.H.

    2007-01-01

    We conducted a three-year study to describe the ecology and behavior of the Midget Faded Rattlesnake, Crotalus organus concolor. We encountered 426 and telemetered 50 C. o. concolor between 2000 and 2002. We found that their primary diet was lizards (associated with rock outcrops), though they will consume small mammals and birds. They den in aggregations, although in low numbers when compared to other subspecies. Movements and activity ranges were among the largest reported for rattlesnakes. Minimum convex polygon area was 117.8 ha for males, 63.9 ha for nongravid females, and 4.8 ha for gravid females. Mean distances traveled per year were 2122.0 m for males, 1956.0 m for nongravid females, and 296.7 m for gravid and postpartum females. Following emergence from hibernation, they spent several weeks shedding, often in aggregations before migration, and migrations occurred in early summer. Most snakes made straight-line movements to and from discrete summer activity ranges where short, multidirectional movements ensued, although others made multidirectional movements throughout the active season. We observed mating behavior between 21 July and 12 August. Gravid females gave birth during the third week of August. Mean clutch size was 4.17 (range 2-7). We found that the sex ratio was skewed favoring females 1:1.24, and they were sexually dimorphic in size (males SVL = 44.1 cm; females SVL = 40.8 cm). Our data further illustrate the diversity within the large group of Western Rattlesnakes (Crotalus viridis). Copyright 2007 Society for the Study of Amphibians and Reptiles.

  2. The Fading of Transient Anomalous X-Ray Pulsar XTE J1810-197

    NASA Astrophysics Data System (ADS)

    Halpern, J. P.; Gotthelf, E. V.

    2005-01-01

    Three observations of the 5.54 s transient anomalous X-ray pulsar XTE J1810-197 obtained over 6 months with the Newton X-ray Multi-Mirror (XMM-Newton) mission are used to study its spectrum and pulsed light curve as the source fades from outburst. The decay is consistent with an exponential of time constant ~300 days but not a power law as predicted in some models of sudden deep crustal heating events. All spectra are well fitted by a blackbody plus a steep power law, a problematic model that is commonly fitted to anomalous X-ray pulsars (AXPs). A two-temperature blackbody fit is also acceptable and better motivated physically in view of the faint optical/IR fluxes, the X-ray pulse shapes that weakly depend on energy in XTE J1810-197, and the inferred emitting areas that are less than or equal to the surface area of a neutron star. The fitted temperatures remained the same while the flux declined by 46%, which can be interpreted as a decrease in area of the emitting regions. The pulsar continues to spin down, albeit at a reduced rate of (5.1+/-1.6)×10-12 s s-1. The inferred characteristic age τc≡P/2P~17,000 yr, magnetic field strength Bs~1.7×1014 G, and outburst properties are consistent with both the outburst and quiescent X-ray luminosities being powered by magnetic field decay, i.e., XTE J1810-197 is a magnetar.

  3. Wireless Channel Characterization: Modeling the 5 GHz Microwave Landing System Extension Band for Future Airport Surface Communications

    NASA Technical Reports Server (NTRS)

    Matolak, D. W.; Apaza, Rafael; Foore, Lawrence R.

    2006-01-01

    We describe a recently completed wideband wireless channel characterization project for the 5 GHz Microwave Landing System (MLS) extension band, for airport surface areas. This work included mobile measurements at large and small airports, and fixed point-to-point measurements. Mobile measurements were made via transmission from the air traffic control tower (ATCT), or from an airport field site (AFS), to a receiving ground vehicle on the airport surface. The point-to-point measurements were between ATCT and AFSs. Detailed statistical channel models were developed from all these measurements. Measured quantities include propagation path loss and power delay profiles, from which we obtain delay spreads, frequency domain correlation (coherence bandwidths), fading amplitude statistics, and channel parameter correlations. In this paper we review the project motivation, measurement coordination, and illustrate measurement results. Example channel modeling results for several propagation conditions are also provided, highlighting new findings.

  4. Optimal channels for channelized quadratic estimators.

    PubMed

    Kupinski, Meredith K; Clarkson, Eric

    2016-06-01

    We present a new method for computing optimized channels for estimation tasks that is feasible for high-dimensional image data. Maximum-likelihood (ML) parameter estimates are challenging to compute from high-dimensional likelihoods. The dimensionality reduction from M measurements to L channels is a critical advantage of channelized quadratic estimators (CQEs), since estimating likelihood moments from channelized data requires smaller sample sizes and inverting a smaller covariance matrix is easier. The channelized likelihood is then used to form ML estimates of the parameter(s). In this work we choose an imaging example in which the second-order statistics of the image data depend upon the parameter of interest: the correlation length. Correlation lengths are used to approximate background textures in many imaging applications, and in these cases an estimate of the correlation length is useful for pre-whitening. In a simulation study we compare the estimation performance, as measured by the root-mean-squared error (RMSE), of correlation length estimates from CQE and power spectral density (PSD) distribution fitting. To abide by the assumptions of the PSD method we simulate an ergodic, isotropic, stationary, and zero-mean random process. These assumptions are not part of the CQE formalism. The CQE method assumes a Gaussian channelized likelihood that can be a valid for non-Gaussian image data, since the channel outputs are formed from weighted sums of the image elements. We have shown that, for three or more channels, the RMSE of CQE estimates of correlation length is lower than conventional PSD estimates. We also show that computing CQE by using a standard nonlinear optimization method produces channels that yield RMSE within 2% of the analytic optimum. CQE estimates of anisotropic correlation length estimation are reported to demonstrate this technique on a two-parameter estimation problem. PMID:27409452

  5. Ion channels and cancer.

    PubMed

    Kunzelmann, Karl

    2005-06-01

    Membrane ion channels are essential for cell proliferation and appear to have a role in the development of cancer. This has initially been demonstrated for potassium channels and is meanwhile also suggested for other cation channels and Cl- channels. For some of these channels, like voltage-gated ether à go-go and Ca2+-dependent potassium channels as well as calcium and chloride channels, a cell cycle-dependent function has been demonstrated. Along with other membrane conductances, these channels control the membrane voltage and Ca2+ signaling in proliferating cells. Homeostatic parameters, such as the intracellular ion concentration, cytosolic pH and cell volume, are also governed by the activity of ion channels. Thus it will be an essential task for future studies to unravel cell cycle-specific effects of ion channels and non-specific homeostatic functions. When studying the role of ion channels in cancer cells, it is indispensable to choose experimental conditions that come close to the in vivo situation. Thus, environmental parameters, such as low oxygen pressure, acidosis and exposure to serum proteins, have to be taken into account. In order to achieve clinical application, more studies on the original cancer tissue are required, and improved animal models. Finally, it will be essential to generate more potent and specific inhibitors of ion channels to overcome the shortcomings of some of the current approaches.

  6. Ion channels in plants

    PubMed Central

    Baluška, František; Mancuso, Stefano

    2013-01-01

    In his recent opus magnum review paper published in the October issue of Physiology Reviews, Rainer Hedrich summarized the field of plant ion channels.1 He started from the earliest electric recordings initiated by Charles Darwin of carnivorous Dionaea muscipula,1,2 known as Venus flytrap, and covered the topic extensively up to the most recent discoveries on Shaker-type potassium channels, anion channels of SLAC/SLAH families, and ligand-activated channels of glutamate receptor-like type (GLR) and cyclic nucleotide-gated channels (CNGC).1 PMID:23221742

  7. Cardiac ion channels

    PubMed Central

    Priest, Birgit T; McDermott, Jeff S

    2015-01-01

    Ion channels are critical for all aspects of cardiac function, including rhythmicity and contractility. Consequently, ion channels are key targets for therapeutics aimed at cardiac pathophysiologies such as atrial fibrillation or angina. At the same time, off-target interactions of drugs with cardiac ion channels can be the cause of unwanted side effects. This manuscript aims to review the physiology and pharmacology of key cardiac ion channels. The intent is to highlight recent developments for therapeutic development, as well as elucidate potential mechanisms for drug-induced cardiac side effects, rather than present an in-depth review of each channel subtype. PMID:26556552

  8. Nova Aquilae 1918 (V603 Aql) Faded by 0.44 MAG Per Century from 1938 to 2013

    NASA Astrophysics Data System (ADS)

    Johnson, Christopher B.; Schaefer, Bradley E.; Kroll, Peter; Henden, Arne A.

    2014-01-01

    We present the light curve of the old nova V603 Aql (Nova Aql 1918) from 1898-1918 and 1934-2013 using 22,721 archival magnitudes. All of our magnitudes are either in, or accurately transformed into, the Johnson B and V magnitude systems. This is vital because offsets in old sequences and the visual-to-V transformation can cause errors of 0.1-1.0 mag if not corrected. Our V603 Aql light curve is the first time that this has been done for any nova. Our goal was to see the evolution of the mass accretion rate on a century timescale, and to test the long-standing prediction of the Hibernation model that old novae should be fading significantly in the century after their eruption is over. The 1918 nova eruption was completely finished by 1938 when the nova decline stopped, and when the star had faded to fainter than its pre-nova brightness of B = 11.43 ± 0.03 mag. We find that the nova light from 1938 to 2013 was significantly fading, with this being seen consistently in three independent data sets (the Sonneberg plates in B, the American Association of Variable Star Observers (AAVSO) V light curve, and the non-AAVSO V light curve). We find that V603 Aql has been declining in brightness at an average rate of 0.44 ± 0.04 mag per century since 1938. This work provides remarkable confirmation of an important prediction of the Hibernation model.

  9. NOVA AQUILAE 1918 (V603 Aql) FADED BY 0.44 MAG PER CENTURY FROM 1938 TO 2013

    SciTech Connect

    Johnson, Christopher B.; Schaefer, Bradley E.; Kroll, Peter; Henden, Arne A.

    2014-01-10

    We present the light curve of the old nova V603 Aql (Nova Aql 1918) from 1898-1918 and 1934-2013 using 22,721 archival magnitudes. All of our magnitudes are either in, or accurately transformed into, the Johnson B and V magnitude systems. This is vital because offsets in old sequences and the visual-to-V transformation can cause errors of 0.1-1.0 mag if not corrected. Our V603 Aql light curve is the first time that this has been done for any nova. Our goal was to see the evolution of the mass accretion rate on a century timescale, and to test the long-standing prediction of the Hibernation model that old novae should be fading significantly in the century after their eruption is over. The 1918 nova eruption was completely finished by 1938 when the nova decline stopped, and when the star had faded to fainter than its pre-nova brightness of B = 11.43 ± 0.03 mag. We find that the nova light from 1938 to 2013 was significantly fading, with this being seen consistently in three independent data sets (the Sonneberg plates in B, the American Association of Variable Star Observers (AAVSO) V light curve, and the non-AAVSO V light curve). We find that V603 Aql has been declining in brightness at an average rate of 0.44 ± 0.04 mag per century since 1938. This work provides remarkable confirmation of an important prediction of the Hibernation model.

  10. A comparison of results obtained with two subsurface non-isothermal multiphase reactive transport simulators, FADES-CORE and TOUGHREACT

    SciTech Connect

    Juncosa Rivera, Ricardo; Xu, Tianfu; Pruess, Karsten

    2001-01-01

    FADES-CORE and TOUGHREACT are codes used to model the non-isothermal multiphase flow with multicomponent reactive transport in porous media. Different flow and reactive transport problems were used to compare the FADES-CORE and TOUGHREACT codes. These problems take into account the different cases of multiphase flow with and without heat transport, conservative transport, and reactive transport. Consistent results were obtained from both codes, which use different numerical methods to solve the differential equations resulting from the various physicochemical processes. Here we present the results obtained from both codes for various cases. Some results are slightly different with minor discrepancies, which have been remedied, so that both codes would be able to reproduce the same processes using the same parameters. One of the discrepancies found is related to the different calculation for thermal conductivity in heat transport, which affects the calculation of the temperatures, as well as the pH of the reaction of calcite dissolution problem modeled. Therefore it is possible to affirm that the pH is highly sensitive to temperature. Generally speaking, the comparison was concluded to be highly satisfactory, leading to the complete verification of the FADES-CORE code. However, we must keep in mind that, as there are no analytical solutions available with which to verify the codes, the TOUGHREACT code has been thoroughly corroborated, given that the only possible way to prove that the code simulation is correct, is by comparing the results obtained with both codes for the identical problems, or to validate the simulation results with actual measured data.

  11. Segmental noxious versus innocuous electrical stimulation for chronic pain relief and the effect of fading sensation during treatment.

    PubMed

    Defrin, Ruth; Ariel, Efrat; Peretz, Chava

    2005-05-01

    It is not clear whether segmental innocuous stimulation has a stronger analgesic effect than segmental noxious stimulation for chronic pain and whether the fading of current sensation during treatment interferes with the analgesic effect, as suggested by the gate control theory. Electrical stimulation (by way of Interferential Current) applied at the pain area (segmental) was administered to 4 groups of patients with osteoarthritis (OA) knee pain. Two groups were administered with noxious stimulation (30% above pain threshold) and two with innocuous stimulation (30% below pain threshold). In each group half of the patients received a fixed current intensity while the other half raised the intensity continuously during treatment whenever fading of sensation was perceived. Group 5 and 6 received sham stimulation and no treatment, respectively. The outcome measures were: chronic pain intensity, morning stiffness, range of motion (ROM), pain threshold and % pain reduction. Both noxious and innocuous stimulation significantly decreased chronic pain (P<0.001) and morning stiffness (P<0.01) and significantly increased pain threshold (P<0.001) and ROM (P<0.001) compared with the control groups. Nevertheless, noxious stimulation decreased pain intensity (P<0.05) and increased pain threshold (P<0.001) significantly more than innocuous stimulation. No differences in treatment outcomes were found between adjusted and unadjusted stimulation. (a) Interferential current is very effective for chronic OA knee pain, (b) segmental noxious stimulation produces a stronger analgesic effect than segmental innocuous stimulation, (c) the fading of sensation during treatment, does not decrease the analgesic effect. Possible mechanisms explaining the findings are discussed.

  12. C. elegans TRP channels.

    PubMed

    Xiao, Rui; Xu, X Z Shawn

    2011-01-01

    Transient receptor potential (TRP) channels represent a superfamily of cation channels found in all eukaryotes. The C. elegans genome encodes seventeen TRP channels covering all of the seven TRP subfamilies. Genetic analyses in C. elegans have implicated TRP channels in a wide spectrum of behavioral and physiological processes, ranging from sensory transduction (e.g. chemosensation, touch sensation, proprioception and osmosensation) to fertilization, drug dependence, organelle biogenesis, apoptosis, gene expression, and neurotransmitter/hormone release. Many C. elegans TRP channels share similar activation and regulatory mechanisms with their vertebrate counterparts. Studies in C. elegans have also revealed some previously unrecognized functions and regulatory mechanisms of TRP channels. C. elegans represents an excellent genetic model organism for the study of function and regulation of TRP channels in vivo. PMID:21290304

  13. Mechanically Activated Ion Channels

    PubMed Central

    Ranade, Sanjeev S.; Syeda, Ruhma; Patapoutian, Ardem

    2015-01-01

    Mechanotransduction, the conversion of physical forces into biochemical signals, is an essential component of numerous physiological processes including not only conscious senses of touch and hearing, but also unconscious senses such as blood pressure regulation. Mechanically activated (MA) ion channels have been proposed as sensors of physical force, but the identity of these channels and an understanding of how mechanical force is transduced has remained elusive. A number of recent studies on previously known ion channels along with the identification of novel MA ion channels have greatly transformed our understanding of touch and hearing in both vertebrates and invertebrates. Here, we present an updated review of eukaryotic ion channel families that have been implicated in mechanotransduction processes and evaluate the qualifications of the candidate genes according to specified criteria. We then discuss the proposed gating models for MA ion channels and highlight recent structural studies of mechanosensitive potassium channels. PMID:26402601

  14. C. elegans TRP channels

    PubMed Central

    Xiao, Rui; Xu, X.Z. Shawn

    2010-01-01

    TRP (transient receptor potential) channels represent a superfamily of cation channels found in all eukaryotes. The C. elegans genome encodes seventeen TRP channels covering all of the seven TRP subfamilies. Genetic analyses in C. elegans have implicated TRP channels in a wide spectrum of behavioral and physiological processes, ranging from sensory transduction (e.g. chemosensation, touch sensation, proprioception and osmosensation) to fertilization, drug dependence, organelle biogenesis, apoptosis, gene expression, and neurotransmitter/hormone release. Many C. elegans TRP channels share similar activation and regulatory mechanisms with their vertebrate counterparts. Studies in C. elegans have also revealed some previously unrecognized functions and regulatory mechanisms of TRP channels. C. elegans represents an excellent genetic model organism for the study of function and regulation of TRP channels in vivo. PMID:21290304

  15. In-situ X-ray absorption spectroscopy analysis of capacity fade in nanoscale-LiCoO{sub 2}

    SciTech Connect

    Patridge, Christopher J.; Swider-Lyons, Karen E.; Twigg, Mark E.; Ramaker, David E.

    2013-07-15

    The local structure of nanoscale (∼10–40 nm) LiCoO{sub 2} is monitored during electrochemical cycling utilizing in-situ X-ray absorption spectroscopy (XAS). The high surface area of the LiCoO{sub 2} nanoparticles not only enhances capacity fade, but also provides a large signal from the particle surface relative to the bulk. Changes in the nanoscale LiCoO{sub 2} metal-oxide bond lengths, structural disorder, and chemical state are tracked during cycling by adapting the delta mu (Δμ) technique in complement with comprehensive extended X-ray absorption fine structure (EXAFS) modeling. For the first time, we use a Δμ EXAFS method, and by comparison of the difference EXAFS spectra, extrapolate significant coordination changes and reduction of cobalt species with cycling. This combined approach suggests Li–Co site exchange at the surface of the nanoscale LiCoO{sub 2} as a likely factor in the capacity fade and irreversible losses in practical, microscale LiCoO{sub 2}. - Graphical abstract: Electrochemical cycling of Li-ion batteries has strong impact on the structure and integrity of the cathode active material particularly near the surface/electrolyte interface. In developing a new method, we have used in-situ X-ray absorption spectroscopy during electrochemical cycling of nanoscale LiCoO{sub 2} to track changes during charge and discharge and between subsequent cycles. Using difference spectra, several small changes in Co-O bond length, Co-O and Co-Co coordination, and site exchange between Co and Li sites can be tracked. These methods show promise as a new technique to better understand processes which lead to capacity fade and loss in Li-ion batteries. - Highlights: • A new method is developed to understand capacity fade in Li-ion battery cathodes. • Structural changes are tracked during Li intercalation/deintercalation of LiCoO{sub 2}. • Surface structural changes are emphasized using nanoscale-LiCoO{sub 2} and difference spectra. • Full multiple

  16. Discovery of a cosmological, relativistic outburst via its rapidly fading optical emission

    SciTech Connect

    Cenko, S. Bradley; Nugent, Peter E.; Miller, Adam A.; Bloom, Joshua S.; Filippenko, Alexei V.; Kulkarni, S. R.; Horesh, Assaf; Carpenter, John; Perley, Daniel A.; Groot, Paul J.; Hallinan, G.; Corsi, Alessandra; Fox, Derek B.; Frail, Dale A.; Gruber, D.; Rau, Arne; Gal-Yam, Avishay; Ofek, Eran O.; MacLeod, Chelsea L.; Kasliwal, Mansi M.; and others

    2013-06-01

    We report the discovery by the Palomar Transient Factory (PTF) of the transient source PTF11agg, which is distinguished by three primary characteristics: (1) bright (R {sub peak} = 18.3 mag), rapidly fading (ΔR = 4 mag in Δt = 2 days) optical transient emission; (2) a faint (R = 26.2 ± 0.2 mag), blue (g' – R = 0.17 ± 0.29 mag) quiescent optical counterpart; and (3) an associated year-long, scintillating radio transient. We argue that these observed properties are inconsistent with any known class of Galactic transients (flare stars, X-ray binaries, dwarf novae), and instead suggest a cosmological origin. The detection of incoherent radio emission at such distances implies a large emitting region, from which we infer the presence of relativistic ejecta. The observed properties are all consistent with the population of long-duration gamma-ray bursts (GRBs), marking the first time such an outburst has been discovered in the distant universe independent of a high-energy trigger. We searched for possible high-energy counterparts to PTF11agg, but found no evidence for associated prompt emission. We therefore consider three possible scenarios to account for a GRB-like afterglow without a high-energy counterpart: an 'untriggered' GRB (lack of satellite coverage), an 'orphan' afterglow (viewing-angle effects), and a 'dirty fireball' (suppressed high-energy emission). The observed optical and radio light curves appear inconsistent with even the most basic predictions for off-axis afterglow models. The simplest explanation, then, is that PTF11agg is a normal, on-axis long-duration GRB for which the associated high-energy emission was simply missed. However, we have calculated the likelihood of such a serendipitous discovery by PTF and find that it is quite small (≈2.6%). While not definitive, we nonetheless speculate that PTF11agg may represent a new, more common (>4 times the on-axis GRB rate at 90% confidence) class of relativistic outbursts lacking associated high

  17. The probability of epidemic fade-out is non-monotonic in transmission rate for the Markovian SIR model with demography.

    PubMed

    Ballard, P G; Bean, N G; Ross, J V

    2016-03-21

    Epidemic fade-out refers to infection elimination in the trough between the first and second waves of an outbreak. The number of infectious individuals drops to a relatively low level between these waves of infection, and if elimination does not occur at this stage, then the disease is likely to become endemic. For this reason, it appears to be an ideal target for control efforts. Despite this obvious public health importance, the probability of epidemic fade-out is not well understood. Here we present new algorithms for approximating the probability of epidemic fade-out for the Markovian SIR model with demography. These algorithms are more accurate than previously published formulae, and one of them scales well to large population sizes. This method allows us to investigate the probability of epidemic fade-out as a function of the effective transmission rate, recovery rate, population turnover rate, and population size. We identify an interesting feature: the probability of epidemic fade-out is very often greatest when the basic reproduction number, R0, is approximately 2 (restricting consideration to cases where a major outbreak is possible, i.e., R0>1). The public health implication is that there may be instances where a non-lethal infection should be allowed to spread, or antiviral usage should be moderated, to maximise the chance of the infection being eliminated before it becomes endemic.

  18. Tracking performance of a combined Costas/AFC-loop under noisy Rayleigh/Rician channel conditions with additive Gaussian noise jamming

    NASA Astrophysics Data System (ADS)

    Kleine, Achim

    Models were developed to investigate the tracking behavior of combined Costas/AFC (Automatic Frequency Control) feedback loops under Rayleigh/Rician fading conditions with additive Gaussian noise jamming. A general linearized tracking model was developed for land-mobile channels. The model can be used for the nonlinearized case with sinusoidal phase detection characteristic using a standard solution of the Fokker-Planck equation. A tracking analysis for Costas/AFC loops with coherent automatic gain control, and an accuracy analysis for interferometers equipped with Costas/AFC loops are treated as examples. The tracking model is the most inaccurate in the case of quasistationary channels.

  19. Experimental study of the helicopter-mobile radioelectrical channel and possible extension to the satellite-mobile channel

    NASA Astrophysics Data System (ADS)

    Blanchetiere-Ciarletti, V.; Sylvain, M.; Lemenn, P.

    1994-07-01

    The use of satellite seems to be an answer to the radioelectrical covering problem for the mobile communications, particularly in the low populated areas. Frequency bands at 1.5 and 2.5 GHz have been dedicated to these future services. Satellite-mobile links will be much more affected by propagation phenomena than the existing links between satellites and fixed stations. The reasons for that are twofold: The probable use of LEO (Low-Earth-Orbit) satellites instead of GEO; such satellites will have to be received at relatively low elevation to limit their number; the use of mobile communication terminals with small and non directive antennas that must work in various environments instead of terrestrian stations located at carefully chosen places and equipped with large diameter paraboloids. These propagation phenomena mainly consist in the fading of the signal level (shadowing of the link), and a frequency selective fading due to multipath propagation. The experience run by C.R.P.E. is aimed at a better understanding of the satellite-mobile propagation channel at fixed frequency as well as on a large band. In this paper, we discuss preliminary results from a series of propagation measurements performed (by lack of any experimental satellite) on an experimental radio link at 1.45 GHz on a of 20 MHz bandwidth between a helicopter flying at a height of 2 km and a mobile receiver. The whole experiment has been run in a rural environment in Brittany (France). In a first part, we illustrate the quality of the data collected during the experiment on a typical case study and give a possible physical interpretation of the observed phenomena. Then we present statistical results concerning the various characteristics (attenuation and delay spreads) of the propagation channel. Finally, we discuss the problem of using a helicopter (flying at a height of 2 km) as a substitute for a satellite at about 1000 km and try to estimate to what extent it is possible to use the data

  20. Rain rate and modeled fade distributions at 20 GHz and 30 GHz derived from five years of network rain gauge measurements

    NASA Technical Reports Server (NTRS)

    Goldhirsh, Julius; Krichevsky, Vladimir; Gebo, Norman

    1992-01-01

    Five years of rain rate and modeled slant path attenuation distributions at 20 GHz and 30 GHz derived from a network of 10 tipping bucket rain gages was examined. The rain gage network is located within a grid 70 km north-south and 47 km east-west in the Mid-Atlantic coast of the United States in the vicinity of Wallops Island, Virginia. Distributions were derived from the variable integration time data and from one minute averages. It was demonstrated that for realistic fade margins, the variable integration time results are adequate to estimate slant path attenuations at frequencies above 20 GHz using models which require one minute averages. An accurate empirical formula was developed to convert the variable integration time rain rates to one minute averages. Fade distributions at 20 GHz and 30 GHz were derived employing Crane's Global model because it was demonstrated to exhibit excellent accuracy with measured COMSTAR fades at 28.56 GHz.

  1. Jamming in Vertical Channels

    NASA Astrophysics Data System (ADS)

    Baxter, G. William; Steel, Fiona

    2011-03-01

    We study jamming of low aspect-ratio cylindrical Delrin grains in a vertical channel. Grain heights are less than their diameter so the grains resemble antacid tablets, coins, or poker chips. These grains are allowed to fall through a vertical channel with a square cross section where the channel width is greater than the diameter of a grain and constant throughout the length of the channel with no obstructions or constrictions. Grains are sometimes observed to form jams, stable structures supported by the channel walls with no support beneath them. The probability of jam occurrence and the strength or robustness of a jam is effected by grain and channel sizes. We will present experimental measurements of the jamming probability and jam strength in this system and discuss the relationship of these results to other experiments and theories. Supported by an Undergraduate Research Grant from Penn State Erie, The Behrend College.

  2. Mechanosensitive channels in microbes.

    PubMed

    Kung, Ching; Martinac, Boris; Sukharev, Sergei

    2010-01-01

    All cells, including microbes, detect and respond to mechanical forces, of which osmotic pressure is most ancient and universal. Channel proteins have evolved such that they can be directly stretched open when the membrane is under turgor pressure. Osmotic downshock, as in rain, opens bacterial mechanosensitive (MS) channels to jettison osmolytes, relieving pressure and preventing cell lysis. The ion flux through individual channel proteins can be observed directly with a patch clamp. MS channels of large and small conductance (MscL and MscS, respectively) have been cloned, crystallized, and subjected to biophysical and genetic analyses in depth. They are now models to scrutinize how membrane forces direct protein conformational changes. Eukaryotic microbes have homologs from animal sensory channels of the TRP superfamily. The MS channel in yeast is also directly sensitive to membrane stretch. This review examines the key concept that proteins embedded in the lipid bilayer can respond to the changes in the mechanical environment the lipid bilayer provides.

  3. Amyloid peptide channels.

    PubMed

    Kagan, B L; Azimov, R; Azimova, R

    2004-11-01

    At least 16 distinct clinical syndromes including Alzheimer's disease (AD), Parkinson's disease (PD), rheumatoid arthritis, type II diabetes mellitus (DM), and spongiform encephelopathies (prion diseases), are characterized by the deposition of amorphous, Congo red-staining deposits known as amyloid. These "misfolded" proteins adopt beta-sheet structures and aggregate spontaneously into similar extended fibrils despite their widely divergent primary sequences. Many, if not all, of these peptides are capable of forming ion-permeable channels in vitro and possibly in vivo. Common channel properties include irreversible, spontaneous insertion into membranes, relatively large, heterogeneous single-channel conductances, inhibition of channel formation by Congo red, and blockade of inserted channels by Zn2+. Physiologic effects of amyloid, including Ca2+ dysregulation, membrane depolarization, mitochondrial dysfunction, inhibition of long-term potentiation (LTP), and cytotoxicity, suggest that channel formation in plasma and intracellular membranes may play a key role in the pathophysiology of the amyloidoses. PMID:15702375

  4. Diagnostic evaluation of power fade phenomena and calendar lifereduction in high-power lithium-ion batteries

    SciTech Connect

    Kostecki, Robert; McLarnon, Frank

    2004-05-01

    High-power Li-ion cells with graphite anodes and LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathodes that were cycled and stored at elevated temperatures showed a significant impedance rise and capacity fade, which were associated primarily with the LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathode. A combination of electrochemical, physical, and chemical diagnostic techniques, including Raman, SEM, and current-sensing AFM, was used to characterize the cathodes from these cells in order to produce a clear picture of the mechanism for cell degradation. Systematic Raman mapping of 50 x 80 {mu}m areas at 0.9 {mu}m spatial resolution produced semi-quantitative composition maps of cathode surfaces. Raman microscopy surface composition maps and SEM images of cathodes from tested cells revealed that cell cycling or storage at elevated temperatures led to significant changes in the LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2}/elemental-carbon surface concentration ratio. The loss of conductive carbon correlated with the power and capacity fade of the tested cathodes and the loss of surface electronic conductivity.

  5. FPGA implementation of dynamic channel assignment algorithm for cognitive wireless sensor networks

    NASA Astrophysics Data System (ADS)

    Martínez, Daniela M.; Andrade, Ángel G.

    2015-07-01

    The reliability of wireless sensor networks (WSNs) in industrial applications can be thwarted due to multipath fading, noise generated by industrial equipment or heavy machinery and particularly by the interference generated from other wireless devices operating in the same spectrum band. Recently, cognitive WSNs (CWSNs) were proposed to improve the performance and reliability of WSNs in highly interfered and noisy environments. In this class of WSN, the nodes are spectrum aware, that is, they monitor the radio spectrum to find channels available for data transmission and dynamically assign and reassign nodes to low-interference condition channels. In this work, we present the implementation of a channel assignment algorithm in a field-programmable gate array, which dynamically assigns channels to sensor nodes based on the interference and noise levels experimented in the network. From the results obtained from the performance evaluation of the CWSN when the channel assignment algorithm is considered, it is possible to identify how many channels should be available in the network in order to achieve a desired percentage of successful transmissions, subject to constraints on the signal-to-interference plus noise ratio on each active link.

  6. Channel-Based Key Generation for Encrypted Body-Worn Wireless Sensor Networks.

    PubMed

    Van Torre, Patrick

    2016-09-08

    Body-worn sensor networks are important for rescue-workers, medical and many other applications. Sensitive data are often transmitted over such a network, motivating the need for encryption. Body-worn sensor networks are deployed in conditions where the wireless communication channel varies dramatically due to fading and shadowing, which is considered a disadvantage for communication. Interestingly, these channel variations can be employed to extract a common encryption key at both sides of the link. Legitimate users share a unique physical channel and the variations thereof provide data series on both sides of the link, with highly correlated values. An eavesdropper, however, does not share this physical channel and cannot extract the same information when intercepting the signals. This paper documents a practical wearable communication system implementing channel-based key generation, including an implementation and a measurement campaign comprising indoor as well as outdoor measurements. The results provide insight into the performance of channel-based key generation in realistic practical conditions. Employing a process known as key reconciliation, error free keys are generated in all tested scenarios. The key-generation system is computationally simple and therefore compatible with the low-power micro controllers and low-data rate transmissions commonly used in wireless sensor networks.

  7. Channel-Based Key Generation for Encrypted Body-Worn Wireless Sensor Networks

    PubMed Central

    Van Torre, Patrick

    2016-01-01

    Body-worn sensor networks are important for rescue-workers, medical and many other applications. Sensitive data are often transmitted over such a network, motivating the need for encryption. Body-worn sensor networks are deployed in conditions where the wireless communication channel varies dramatically due to fading and shadowing, which is considered a disadvantage for communication. Interestingly, these channel variations can be employed to extract a common encryption key at both sides of the link. Legitimate users share a unique physical channel and the variations thereof provide data series on both sides of the link, with highly correlated values. An eavesdropper, however, does not share this physical channel and cannot extract the same information when intercepting the signals. This paper documents a practical wearable communication system implementing channel-based key generation, including an implementation and a measurement campaign comprising indoor as well as outdoor measurements. The results provide insight into the performance of channel-based key generation in realistic practical conditions. Employing a process known as key reconciliation, error free keys are generated in all tested scenarios. The key-generation system is computationally simple and therefore compatible with the low-power micro controllers and low-data rate transmissions commonly used in wireless sensor networks. PMID:27618051

  8. Channel-Based Key Generation for Encrypted Body-Worn Wireless Sensor Networks.

    PubMed

    Van Torre, Patrick

    2016-01-01

    Body-worn sensor networks are important for rescue-workers, medical and many other applications. Sensitive data are often transmitted over such a network, motivating the need for encryption. Body-worn sensor networks are deployed in conditions where the wireless communication channel varies dramatically due to fading and shadowing, which is considered a disadvantage for communication. Interestingly, these channel variations can be employed to extract a common encryption key at both sides of the link. Legitimate users share a unique physical channel and the variations thereof provide data series on both sides of the link, with highly correlated values. An eavesdropper, however, does not share this physical channel and cannot extract the same information when intercepting the signals. This paper documents a practical wearable communication system implementing channel-based key generation, including an implementation and a measurement campaign comprising indoor as well as outdoor measurements. The results provide insight into the performance of channel-based key generation in realistic practical conditions. Employing a process known as key reconciliation, error free keys are generated in all tested scenarios. The key-generation system is computationally simple and therefore compatible with the low-power micro controllers and low-data rate transmissions commonly used in wireless sensor networks. PMID:27618051

  9. HIPPI and Fibre Channel

    SciTech Connect

    Tolmie, D.E.

    1992-01-01

    The High-Performance Parallel Interface (HIPPI) and Fibre Channel are near-gigabit per second data communications interfaces being developed in ANSI standards Task Group X3T9.3. HIPPI is the current interface of choice in the high-end and supercomputer arena, and Fibre Channel is a follow-on effort. HIPPI came from a local area network background, and Fibre Channel came from a mainframe to peripheral interface background.

  10. Train-of-four fade during neuromuscular blockade induced by tubocurarine, succinylcholine or alpha-bungarotoxin in the rat isolated hemidiaphragm.

    PubMed

    Cheah, L S; Gwee, M C

    1988-12-01

    1. Nerve-evoked maximal twitches (T1, T2, T3, T4) of the rat isolated hemidiaphragm to train-of-four (TOF) stimulation (2 Hz X 2 s) were recorded continuously in the absence or presence of tubocurarine (1.5 mumol/l), succinylcholine (40 mumol/l) or alpha-bungarotoxin (1 mumol/l). The T1 and T4 response-time profiles for the three drugs were analysed with respect to amplitude depression and the TOF ratio (T4/T1) during the development of and recovery from neuromuscular blockade. 2. Tubocurarine produced T1 block accompanied by intense TOF fade; for the same degree of T1 block, the TOF ratio was lower during the recovery from blockade after washing out tubocurarine from the bath than during the onset of blockade. There was also a correspondingly slower recovery of the TOF ratio from 90% T1 block to control levels when compared with the time for complete T1 recovery. Fade and twitch tension depression were shown clearly to be separate responses, each with its own response-time profile. Fade is therefore not simply a consequence of postjunctional cholinoceptor blockade. 3. Succinylcholine produced T1 block with only moderate TOF fade; similar recovery rates from 90% T1 block to control levels were obtained for T1 and the TOF ratio. 4. alpha-Bungarotoxin produced irreversible and complete neuromuscular blockade during which TOF fade was virtually absent. 5. The results obtained in this study closely resemble those from other similar studies in animals and in humans and clearly demonstrate that the rat isolated hemidiaphragm is a suitable in vitro model for time course studies on TOF fade.

  11. Symmetrization for redundant channels

    NASA Technical Reports Server (NTRS)

    Tulplue, Bhalchandra R. (Inventor); Collins, Robert E. (Inventor)

    1988-01-01

    A plurality of redundant channels in a system each contain a global image of all the configuration data bases in each of the channels in the system. Each global image is updated periodically from each of the other channels via cross channel data links. The global images of the local configuration data bases in each channel are separately symmetrized using a voting process to generate a system signal configuration data base which is not written into by any other routine and is available for indicating the status of the system within each channel. Equalization may be imposed on a suspect signal and a number of chances for that signal to heal itself are provided before excluding it from future votes. Reconfiguration is accomplished upon detecting a channel which is deemed invalid. A reset function is provided which permits an externally generated reset signal to permit a previously excluded channel to be reincluded within the system. The updating of global images and/or the symmetrization process may be accomplished at substantially the same time within a synchronized time frame common to all channels.

  12. Phosphoinositides regulate ion channels

    PubMed Central

    Hille, Bertil; Dickson, Eamonn J.; Kruse, Martin; Vivas, Oscar; Suh, Byung-Chang

    2014-01-01

    Phosphoinositides serve as signature motifs for different cellular membranes and often are required for the function of membrane proteins. Here, we summarize clear evidence supporting the concept that many ion channels are regulated by membrane phosphoinositides. We describe tools used to test their dependence on phosphoinositides, especially phosphatidylinositol 4,5-bisphosphate, and consider mechanisms and biological meanings of phosphoinositide regulation of ion channels. This lipid regulation can underlie changes of channel activity and electrical excitability in response to receptors. Since different intracellular membranes have different lipid compositions, the activity of ion channels still in transit towards their final destination membrane may be suppressed until they reach an optimal lipid environment. PMID:25241941

  13. IBEX channel formation

    SciTech Connect

    Jones, E.E.; Frost, C.A.; Freeman, J.R.; Jojola, J.M.

    1987-01-01

    Exploding wire experiments have been conducted to form a low-density channel for endoatmospheric channel-tracking experiments to be performed on the IBEX accelerator. Stainless steel and tungsten wires as small as six microns radius have been exploded using a 50 kJ, 200 kV fast capacitor bank designed and constructed for the purpose. Density channels have been produced. Preliminary results will be compared with a simple circuit model and hydrocode analysis. Efforts to diagnose the low-density channel are beginning. 5 refs.

  14. Demodulation Algorithms for the Ofdm Signals in the Time- and Frequency-Scattering Channels

    NASA Astrophysics Data System (ADS)

    Bochkov, G. N.; Gorokhov, K. V.; Kolobkov, A. V.

    2016-06-01

    We consider a method based on the generalized maximum-likelihood rule for solving the problem of reception of the signals with orthogonal frequency division multiplexing of their harmonic components (OFDM signals) in the time- and frequency-scattering channels. The coherent and incoherent demodulators effectively using the time scattering due to the fast fading of the signal are developed. Using computer simulation, we performed comparative analysis of the proposed algorithms and well-known signal-reception algorithms with equalizers. The proposed symbolby-symbol detector with decision feedback and restriction of the number of searched variants is shown to have the best bit-error-rate performance. It is shown that under conditions of the limited accuracy of estimating the communication-channel parameters, the incoherent OFDMsignal detectors with differential phase-shift keying can ensure a better bit-error-rate performance compared with the coherent OFDM-signal detectors with absolute phase-shift keying.

  15. Presynaptic muscarinic and adenosine receptors are involved in 2 Hz-induced train-of-four fade caused by antinicotinic neuromuscular relaxants in the rat.

    PubMed

    Pereira, Mw; Bornia, Ecs; Correia-de-Sá, P; Alves-Do-Prado, W

    2011-11-01

    1. Train-of-four fade (TOF(fade) ) is a clinically useful parameter to monitor the degree of block of neuromuscular transmission in curarized patients. Experimentally, TOF(fade) has been attributed to the blockade of facilitatory nicotinic receptors on motor nerve terminals. There is less information regarding the involvement of coexistent presynaptic receptors (e.g. muscarinic M(1) and M(2) , adenosine A(1) and A(2A) ) in the TOF(fade) produced by antinicotinic agents. 2. In the present study, we evaluated the TOF(fade) caused by antinicotinic neuromuscular relaxants (hexamethonium, d-tubocurarine, vecuronium and rocuronium) as the ratio of the muscle tension produced in the rat diaphragm by the fourth to the first stimulus (T(4) /T(1) ) of a train-of-four stimuli delivered to the phrenic nerve trunk at a frequency of 2 Hz. 3. All antinicotinic agents, except hexamethonium, decreased the amplitude of muscle tension during the first stimulus. Hexamethonium, (5.47 mmol/L), d-tubocurarine- (1.1 μmol/L), vecuronium (4.7 μmol/L)- and rocuronium (9.8 μmol/L)-induced TOF(fade) was attenuated by 10 nmol/L pirenzepine (an M(1) receptor antagonist), 1 μmol/L methoctramine (an M(2) receptor antagonist) and 2.5 nmol/L 1,3-dipropyl-8-cyclopentylxanthine (an A(1) receptor antagonist). Blockade of the A(2A) receptor with 10 nmol/L ZM241385 partially reversed the TOF(fade) induced by d-tubocurarine, vecuronium and rocuronium, but not that caused by the 'pure' neuronal nicotinic receptor antagonist hexamethonium, unless one increased the concentration of ZM241385 to 50 nmol/L. 4. The data indicate that presynaptic M(1) , M(2) , A(1) and A(2A) receptors play a role in neuromuscular TOF(fade) caused by antinicotinic neuromuscular relaxants. Such interplay depends on adenosine tonus and on the affinity of neuromuscular blocking agents for neuronal versus muscular nicotinic receptors.

  16. SU-E-T-222: Investigation of Pre and Post Irradiation Fading of the TLD100 Thermoluminescence Dosimetry for Photon Beams

    SciTech Connect

    Sina, S; Sadeghi, M; Faghihi, R

    2014-06-01

    Purpose: The pre-irradiation and post-irradiation fading of the Thermoluminescense dosimeter signals were investigated in this study. Methods: Two groups of TLD chips with pre-determined ECC values were used in this study. The two groups were divided into 6 series, each composing of 5 TLD chips.The first group was used for pre-irradiation fading. 5 TLDs were exposed to a known amount of radiation from Cs-137 source, and were read out the next day. After seven days, the other 5 TLDs were exposed to the same amount of radiation and were read out after a day. The other series of 5 TLDs were also exposed after 7,19,28, 59, and 90 days, and were read out a day after irradiation. The loss in TLD signal were obtained for all the above cases. The second group, was used for postirradiation fading. All the TLDs of this group were exposed to a known amount of radiation from Cs-137 source. The 6 series composed of 5 TLDs were read out after 1,7,19,28,59, and 90 days. The above-mentioned procedures for obtaining pre-irradiation, and post-irradiation fading were performed for three storage temperatures (25°C, 4°C, and −18°C). Results: According to the results obtained in this study, in case of pre-irradiation fading study, the signal losses after 90 days are 12%, 24%, and 17% for 25°C, 4°C, and −18°C respectively. In case of post-irradiation fading study, the sensitivity losses after 90 days are 25%, 216%, and 20% for 25°C, 4°C, and −18°C respectively. Conclusion: The results indicate that the optimized time between exposing and reading out, and also the optimized time between annealing and exposing is 1 day.The reduction of Storage temperature will reduce the post-irradiation fading, While temperature reduction does not have any effect on pre-irradiation fading.

  17. A linearization of quantum channels

    NASA Astrophysics Data System (ADS)

    Crowder, Tanner

    2015-06-01

    Because the quantum channels form a compact, convex set, we can express any quantum channel as a convex combination of extremal channels. We give a Euclidean representation for the channels whose inverses are also valid channels; these are a subset of the extreme points. They form a compact, connected Lie group, and we calculate its Lie algebra. Lastly, we calculate a maximal torus for the group and provide a constructive approach to decomposing any invertible channel into a product of elementary channels.

  18. Basaltic Lava Channels

    NASA Astrophysics Data System (ADS)

    Cashman, K. V.; Griffiths, R. W.; Kerr, R. C.

    2004-12-01

    In Hawaii, the mode of lava transport - through open channels or through insulating lava tubes - determines the thermal, rheological, and emplacement history of a lava flow. Most Hawaiian lavas are erupted at near-liquidus temperatures and are therefore crystal-poor; lava transport through open channels allows rapid cooling and consequent rapid increases in lava crystallinity. Solidified aa flows resulting from channelized flow are typically fine-grained throughout their thickness, indicating cooling of the entire flow thickness during transport. In contrast, transport of lava through insulating tubes permits flow over long distances with little cooling. Flows emerging from such tubes typically have pahoehoe flow surfaces with glassy crusts. Groundmass textures that coarsen from the flow rind to the interior reflect rates of post-emplacement, rather than syn-emplacement, cooling. To distinguish eruption conditions that result in lava channels from those that allow formation of lava tubes, we have performed a series of laboratory experiments involving injection of PEG 600 (a wax with a Newtonian rheology and freezing temperature of 19ºC) into cold water through both uniform and non-uniform sloping channels. In uniform channels, tube formation can be distinguished from open channel flow using a dimensionless parameter based on a solidification time scale, an advection time scale, and a Rayleigh number that describes convection by heat loss from crust-free shear zones. Theoretical analysis predicts that in the open channel regime, the width of the crust (dc) will vary with the channel width (W) as dc = W5/3. Crustal coverage of non-uniform channels in both laboratory experiments and field examples from Kilauea Volcano, Hawaii, is consistent with this prediction. However, experiments in non-uniform channels illustrate additional controls on the surface coverage of lava channels. Most important is crustal extension resulting from flow acceleration through constrictions

  19. Ion channels in microbes

    PubMed Central

    Martinac, Boris; Saimi, Yoshiro; Kung, Ching

    2008-01-01

    Summary Studies of ion channels have for long been dominated by the animalcentric, if not anthropocentric view of physiology. The structures and activities of ion channels had, however, evolved long before the appearance of complex multicellular organisms on Earth. The diversity of ion channels existing in cellular membranes of prokaryotes is a good example. Though at first it may appear as a paradox that most of what we know about the structure of eukaryotic ion channels is based on the structure of bacterial channels, this should not be surprising given the evolutionary relatedness of all living organisms and suitability of microbial cells for structural studies of biological macromolecules in a laboratory environment. Genome sequences of the human as well as various microbial, plant and animal organisms unambiguously established the evolutionary links, whereas crystallographic studies of the structures of major types of ion channels published over the last decade clearly demonstrated the advantage of using microbes as experimental organisms. The purpose of this review is not only to provide an account of acquired knowledge on microbial ion channels but also to show that the study of microbes and their ion channels may also hold a key to solving unresolved molecular mysteries in the future. PMID:18923187

  20. Generalized channeled polarimetry.

    PubMed

    Alenin, Andrey S; Tyo, J Scott

    2014-05-01

    Channeled polarimeters measure polarization by modulating the measured intensity in order to create polarization-dependent channels that can be demodulated to reveal the desired polarization information. A number of channeled systems have been described in the past, but their proposed designs often unintentionally sacrifice optimality for ease of algebraic reconstruction. To obtain more optimal systems, a generalized treatment of channeled polarimeters is required. This paper describes methods that enable handling of multi-domain modulations and reconstruction of polarization information using linear algebra. We make practical choices regarding use of either Fourier or direct channels to make these methods more immediately useful. Employing the introduced concepts to optimize existing systems often results in superficial system changes, like changing the order, orientation, thickness, or spacing of polarization elements. For the two examples we consider, we were able to reduce noise in the reconstruction to 34.1% and 57.9% of the original design values. PMID:24979633

  1. Athermalized channeled spectropolarimeter enhancement.

    SciTech Connect

    Jones, Julia Craven; Way, Brandyn Michael; Mercier, Jeffrey Alan; Hunt, Jeffery P.

    2013-09-01

    Channeled spectropolarimetry can measure the complete polarization state of light as a function of wavelength. Typically, a channeled spectropolarimeter uses high order retarders made of uniaxial crystal to amplitude modulate the measured spectrum with the spectrally-dependent Stokes polarization information. A primary limitation of conventional channeled spectropolarimeters is related to the thermal variability of the retarders. Thermal variation often forces frequent system recalibration, particularly for field deployed systems. However, implementing thermally stable retarders, made of biaxial crystal, results in an athermal channeled spectropolarimeter that relieves the need for frequent recalibration. This report presents experimental results for an anthermalized channeled spectropolarimeter prototype produced using potassium titanyl phosphate. The results of this prototype are compared to the current thermal stabilization state of the art. Finally, the application of the technique to the thermal infrared is studied, and the athermalization concept is applied to an infrared imaging spectropolarimeter design.

  2. Jamming in Vertical Channels

    NASA Astrophysics Data System (ADS)

    Baxter, G. William; McCausland, Jeffrey; Steel, Fiona

    2010-03-01

    We experimentally study jamming of cylindrical grains in a vertical channel. The grains have a low aspect-ratio (height/diameter < 1) so their shape is like antacid tablets or poker chips. They are allowed to fall through a vertical channel with a square cross section. The channel width is greater than the diameter of a grain and constant throughout the length of the channel with no obstructions or constrictions. It is observed that grains sometimes jam in this apparatus. In a jam, grains form a stable structure from one side of the channel to the other with nothing beneath them. Jams may be strong enough to support additional grains above. The probability of a jam occurring is a function of the grain height and diameter. We will present experimental measurements of the jamming probability in this system and discuss the relationship of these results to other experiments and theories.

  3. Joint Transmit Antenna Selection and Power Allocation for ISDF Relaying Mobile-to-Mobile Sensor Networks

    PubMed Central

    Xu, Lingwei; Zhang, Hao; Gulliver, T. Aaron

    2016-01-01

    The outage probability (OP) performance of multiple-relay incremental-selective decode-and-forward (ISDF) relaying mobile-to-mobile (M2M) sensor networks with transmit antenna selection (TAS) over N-Nakagami fading channels is investigated. Exact closed-form OP expressions for both optimal and suboptimal TAS schemes are derived. The power allocation problem is formulated to determine the optimal division of transmit power between the broadcast and relay phases. The OP performance under different conditions is evaluated via numerical simulation to verify the analysis. These results show that the optimal TAS scheme has better OP performance than the suboptimal scheme. Further, the power allocation parameter has a significant influence on the OP performance. PMID:26907282

  4. Joint Transmit Antenna Selection and Power Allocation for ISDF Relaying Mobile-to-Mobile Sensor Networks.

    PubMed

    Xu, Lingwei; Zhang, Hao; Gulliver, T Aaron

    2016-02-19

    The outage probability (OP) performance of multiple-relay incremental-selective decode-and-forward (ISDF) relaying mobile-to-mobile (M2M) sensor networks with transmit antenna selection (TAS) over N-Nakagami fading channels is investigated. Exact closed-form OP expressions for both optimal and suboptimal TAS schemes are derived. The power allocation problem is formulated to determine the optimal division of transmit power between the broadcast and relay phases. The OP performance under different conditions is evaluated via numerical simulation to verify the analysis. These results show that the optimal TAS scheme has better OP performance than the suboptimal scheme. Further, the power allocation parameter has a significant influence on the OP performance.

  5. Joint Transmit Antenna Selection and Power Allocation for ISDF Relaying Mobile-to-Mobile Sensor Networks.

    PubMed

    Xu, Lingwei; Zhang, Hao; Gulliver, T Aaron

    2016-01-01

    The outage probability (OP) performance of multiple-relay incremental-selective decode-and-forward (ISDF) relaying mobile-to-mobile (M2M) sensor networks with transmit antenna selection (TAS) over N-Nakagami fading channels is investigated. Exact closed-form OP expressions for both optimal and suboptimal TAS schemes are derived. The power allocation problem is formulated to determine the optimal division of transmit power between the broadcast and relay phases. The OP performance under different conditions is evaluated via numerical simulation to verify the analysis. These results show that the optimal TAS scheme has better OP performance than the suboptimal scheme. Further, the power allocation parameter has a significant influence on the OP performance. PMID:26907282

  6. Performance analysis of LDPC codes on OOK terahertz wireless channels

    NASA Astrophysics Data System (ADS)

    Chun, Liu; Chang, Wang; Jun-Cheng, Cao

    2016-02-01

    Atmospheric absorption, scattering, and scintillation are the major causes to deteriorate the transmission quality of terahertz (THz) wireless communications. An error control coding scheme based on low density parity check (LDPC) codes with soft decision decoding algorithm is proposed to improve the bit-error-rate (BER) performance of an on-off keying (OOK) modulated THz signal through atmospheric channel. The THz wave propagation characteristics and channel model in atmosphere is set up. Numerical simulations validate the great performance of LDPC codes against the atmospheric fading and demonstrate the huge potential in future ultra-high speed beyond Gbps THz communications. Project supported by the National Key Basic Research Program of China (Grant No. 2014CB339803), the National High Technology Research and Development Program of China (Grant No. 2011AA010205), the National Natural Science Foundation of China (Grant Nos. 61131006, 61321492, and 61204135), the Major National Development Project of Scientific Instrument and Equipment (Grant No. 2011YQ150021), the National Science and Technology Major Project (Grant No. 2011ZX02707), the International Collaboration and Innovation Program on High Mobility Materials Engineering of the Chinese Academy of Sciences, and the Shanghai Municipal Commission of Science and Technology (Grant No. 14530711300).

  7. Fine Channel Networks

    NASA Technical Reports Server (NTRS)

    1997-01-01

    A color image of fine channel networks on Mars; north toward top. The scene shows heavily cratered highlands dissected by dendritic open channel networks that dissect steep slopes of impact crater walls. This image is a composite of Viking high-resolution images in black and white and low-resolution images in color. The image extends from latitude 9 degrees S. to 5 degrees S. and from longitude 312 degrees to 320 degrees; Mercator projection. The dendritic pattern of the fine channels and their location on steep slopes leads to the interpretation that these are runoff channels. The restriction of these types of channels to ancient highland rocks suggests that these channels are old and date from a time on Mars when conditions existed for precipitation to actively erode rocks. After the channels reach a low plain, they appear to end. Termination may have resulted from burial by younger deposits or perhaps the flows percolated into the surface materials and continued underground.

  8. Multi-year slant path rain fade statistics at 28.56 and 19.04 GHz for Wallops Island, Virginia

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1979-01-01

    Multiyear rain fade statistics at 28.56 GHz and 19.04 GHz were compiled for the region of Wallops Island, Virginia covering the time periods, 1 April 1977 through 31 March 1978, and 1 September 1978 through 31 August 1979. The 28.56 GHz attenuations were derived by monitoring the beacon signals from the COMSTAR geosynchronous satellite, D sub 2 during the first year, and satellite, D sub 3, during the second year. Although 19.04 GHz beacons exist aboard these satellites, statistics at this frequency were predicted using the 28 GHz fade data, the measured rain rate distribution, and effective path length concepts. The prediction method used was tested against radar derived fade distributions and excellent comparisons were noted. For example, the rms deviations between the predicted and test distributions were less than or equal to 0.2dB or 4% at 19.04 GHz. The average ratio between the 28.56 GHz and 19.04 GHz fades were also derived for equal percentages of time resulting in a factor of 2.1 with a .05 standard deviation.

  9. Crystal violet: Study of the photo-fading of an early synthetic dye in aqueous solution and on paper with HPLC-PDA, LC-MS and FORS

    NASA Astrophysics Data System (ADS)

    Confortin, Daria; Neevel, Han; Brustolon, Marina; Franco, Lorenzo; Kettelarij, Albert J.; Williams, Renè M.; van Bommel, Maarten R.

    2010-06-01

    The photo-fading of crystal violet (CV), one of the earliest synthetic dyes and an ink component, is examined both in solution and on paper. Aqueous solutions of CV were exposed to UV light (365nm) and samples were taken at constant time intervals and analysed with a High Performance Liquid Chromatography-Photo Diode Array (HPLC-PDA) and Liquid Chromatography-Mass Spectroscopy (LC-MS). Demethylation products were positively identified. Also, deamination probably occurred. The oxidation at the central carbon likely generates Michler's ketone (MK) or its derivatives, but still needs confirmation. To study CV on paper, Whatman paper was immersed in CV and exposed to UV light. Before and after different irradiation periods, reflectance spectra were recorded with Fibre Optic Reflectance Spectrophotometry (FORS). A decrease in CV concentration and a change in aggregation type for CV molecules upon irradiation was observed. Colorimetric L*a*b* values before and during irradiation were also measured. Also, CV was extracted from paper before and after different irradiation periods and analysed with HPLC-PDA. Photo-fading of CV on paper produced the same products as in solution, at least within the first 100 hours of irradiation. Finally, a photo-fading of CV in the presence of MK on Whatman paper was performed. It was demonstrated that MK both accelerates CV degradation and is consumed during the reaction. The degradation pathway identified in this work is suitable for explaining the photo/fading of other dyes belonging to the triarylmethane group.

  10. X-ray photoelectron spectroscopy of negative electrodes from high-power lithium-ion cells showing various levels of power fade

    SciTech Connect

    Herstedt, Marie; Abraham, Daniel P.; Kerr, John B.

    2004-02-28

    High-power lithium-ion cells for transportation applications are being developed and studied at Argonne National Laboratory. The current generation of cells containing LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2}-based cathodes, graphite-based anodes, and LiPF6-based electrolytes show loss of capacity and power during accelerated testing at elevated temperatures. Negative electrode samples harvested from some cells that showed varying degrees of power and capacity fade were examined by X-ray photoelectron spectroscopy (XPS). The samples exhibited a surface film on the graphite, which was thicker on samples from cells that showed higher fade. Furthermore, solvent-based compounds were dominant on samples from low power fade cells, whereas LiPF{sub 6}-based products were dominant on samples from high power fade cells. The effect of sample rinsing and air exposure is discussed. Mechanisms are proposed to explain the formation of compounds suggested by the XPS data.

  11. Impact of Backwards Faded Scaffolding Approach to Inquiry-Based Astronomy Laboratory Experiences on Undergraduate Non-Science Majors' Views of Scientific Inquiry

    ERIC Educational Resources Information Center

    Lyons, Daniel J.

    2011-01-01

    This study explored the impact of a novel inquiry-based astronomy laboratory curriculum designed using the Backwards Faded Scaffolding inquiry teaching framework on non-science majoring undergraduate students' views of the nature of scientific inquiry (NOSI). The study focused on two aspects of NOSI: The Distinction between Data and Evidence…

  12. [DYNAMICS OF GAZE FIXATION DURATION AND EVENT RELATED POTENTIALS WHILE PRESENTATION FADING-IN IMAGES AND DISTRACTORS].

    PubMed

    Koltunova, T I; Podladchikova, L N; Shaposhnikov, D G; Vladimirski, B M; Syrkin, L D; Kruchkov, B I; Usov, V M

    2015-10-01

    A method for studying the dynamics of human visual attention at various stages of image viewing and recognition has been described. The method is based on the presentation of fading-in images and distractors into the foveal part of visual field. Experimental data demonstrate the effect of habituation to the distractor and bimodal distribution of fixation duration in trials with distractor. It is shown that the effect of distractor is dependent on the complexity of the target images. Significant decrease of the latency of component P350 of fixation related potentials while the simultaneous presentation of target images and distractors is detected in the most of EEG recordings except the occipital ones. On the base of the results obtained the development of tests for evaluation of the current state of visual attention of human-operators, whose main current activities must not be disturbed, has been considered.

  13. Origin of Capacity Fading in Nano-Sized Co3O4Electrodes: Electrochemical Impedance Spectroscopy Study

    PubMed Central

    2008-01-01

    Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co3O4, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co3O4with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co3O4anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.

  14. Ice depolarization of the Comstar beacon at 28.56 GHz during low fades and correlation with radar backscatter

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1982-01-01

    Radar correlation with significant ice depolarization events accompanied by low copolarization fades of the 28.56-GHz Comstar beacon signal are described for an experimental program at Wallops Island, VA. Using a Faraday switch at the front end of the receiver, the copolarization and cross-polarization levels of the 28.56-GHz beacon signal are sequentially monitored. A nearby high resolution S-band radar pointing along the earth-satellite path monitors the simultaneous ice and rain reflectivity. For a first case considered, excellent correlation is noted between the cross-polarization events and relatively large and extended ice reflectivities along a segment of the earth-satellite path at altitudes near and above the 0 C isotherm. In a second case, the radar and receiver data strongly suggest the cross-polarization mechanism is due to a hailshaft which intersects the path at altitudes well below the 0 deg isotherm.

  15. Why are Channels Sinuous?

    NASA Astrophysics Data System (ADS)

    Constantine, J. A.; Lazarus, E.

    2012-12-01

    Sinuosity is a ubiquitous property of channelized flow patterns on Earth and other planetary bodies. Sinuosity is typically discussed as an emergent consequence of migration processes in meandering rivers, but meandering rivers are only one type of sinuous channel: there are many examples that show little or no indication of meandering, such as bedrock river canyons, drainage channels in tidal mudflats, and volcanic rilles. In some of these patterns, sinuosity is described as "inherited" from a preexisting morphology, which elides an explanation for how the inherited sinuosity originated. Even in river meandering theory there is ongoing debate regarding how initial channel sinuosity arises. Comparing the results of a generalized flow-routing model to observations of natural flow patterns, we find that the ratio of floodplain resistance (R, representing topographic roughness, substrate erodibility, or vegetation density) relative to floodplain slope (m) produces a range of sinuous planforms with natural analogs. We offer a unifying theory for channel sinuosity in which this ratio of resistance to slope (R:m) exerts the primary landscape control on planform shape and predicts the range of sinuosity a floodplain may express. Resistance-dominated floodplains produce channels with higher sinuosity than those of slope-dominated floodplains because increased resistance impedes down-slope flow. Measurement of "relative resistance" (R:m) could inform how riparian restoration projects evaluate the floodplains of artificially straightened rivers. Our analysis suggests that if the sinuosity of a formerly natural channel derived from a high R:m, then even a channel redesigned to be sinuous will straighten if the relative resistance of its floodplain is suppressed or inherently low. (Alternatively, increasing floodplain resistance might foster a higher sinuosity than hydraulic geometry would forecast.) The explanation for sinuosity that we propose is universal enough to account

  16. Video coding with fixed-length packetization for a tandem channel.

    PubMed

    Shen, Yushi; Cosman, Pamela C; Milstein, Laurence B

    2006-02-01

    A robust scheme is presented for the efficient transmission of packet video over a tandem wireless Internet channel. This channel is assumed to have bit errors (due to noise and fading on the wireless portion of the channel) and packet erasures (due to congestion on the wired portion). First, we propose an algorithm to optimally switch between intracoding and intercoding for a video coder that operates on a packet-switched network with fixed-length packets. Different re-synchronization schemes are considered and compared. This optimal mode selection algorithm is integrated with an efficient channel encoder, a cyclic redundancy check outer coder concatenated with an inner rate-compatible punctured convolutional coder. The system performance is both analyzed and simulated. Last, the framework is extended to operate on a time-varying wireless Internet channel with feedback information from the receiver. Both instantaneous feedback and delayed feedback are evaluated, and an improved method of refined distortion estimation for encoding is presented and simulated for the case of delayed feedback.

  17. Fractional channel multichannel analyzer

    DOEpatents

    Brackenbush, Larry W.; Anderson, Gordon A.

    1994-01-01

    A multichannel analyzer incorporating the features of the present invention obtains the effect of fractional channels thus greatly reducing the number of actual channels necessary to record complex line spectra. This is accomplished by using an analog-to-digital converter in the asynscronous mode, i.e., the gate pulse from the pulse height-to-pulse width converter is not synchronized with the signal from a clock oscillator. This saves power and reduces the number of components required on the board to achieve the effect of radically expanding the number of channels without changing the circuit board.

  18. Channel Access in Erlang

    SciTech Connect

    Nicklaus, Dennis J.

    2013-10-13

    We have developed an Erlang language implementation of the Channel Access protocol. Included are low-level functions for encoding and decoding Channel Access protocol network packets as well as higher level functions for monitoring or setting EPICS process variables. This provides access to EPICS process variables for the Fermilab Acnet control system via our Erlang-based front-end architecture without having to interface to C/C++ programs and libraries. Erlang is a functional programming language originally developed for real-time telecommunications applications. Its network programming features and list management functions make it particularly well-suited for the task of managing multiple Channel Access circuits and PV monitors.

  19. A method to minimise the fading effects of LiF:Mg,Ti (TLD-600 and TLD-700) using a pre-heat technique.

    PubMed

    Lee, YoungJu; Won, Yuho; Kang, Kidoo

    2015-04-01

    Passive integrating dosemeters [thermoluminescent dosimeter (TLD) and optically stimulated luminescence (OSL)] are the only legally permitted individual dosemeters for occupational external radiation exposure monitoring in Korea. Also its maximum issuing cycle does not exceed 3 months, and the Korean regulations require personal dosemeters for official assessment of external radiation exposure to be issued by an approved or rather an accredited dosimetry service according to ISO/IEC 17025. KHNP (Korea Hydro & Nuclear Power, LTD), a unique operating company of nuclear power plants (NPPs) in Korea, currently has a plan to extend a TLD issuing cycle from 1 to 3 months under the authors' fading error criteria, ±10%. The authors have performed a feasibility study that minimises post-irradiation fading effects within their maximum reading cycle employing pre-heating technique. They repeatedly performed irradiation/reading a bare TLD chip to determine optimum pre-heating conditions by analysing each glow curve. The optimum reading conditions within the maximum reading cycle of 3 months were decided: a pre-heating temperature of 165°C, a pre-heating time of 9 s, a heating rate of 25°C s(-1), a reading temperature of 300°C and an acquisition time of 10 s. The fading result of TLD-600 and TLD-700 carried by newly developed time temperature profile (TTP) showed a much smaller fading effect than that of current TTP. The result showed that the fading error due to a developed TTP resulted in a ∼5% signal loss, whereas a current TTP caused a ∼15% loss. The authors also carried out a legal performance test on newly developed TTP to confirm its possibility as an official dosemeter. The legal performance tests that applied the developed TTP satisfied the criteria for all the test categories. PMID:25301971

  20. Calcium Channel Signaling Complexes with Receptors and Channels.

    PubMed

    Zamponi, Gerald W

    2015-01-01

    Voltage-gated calcium channels are not only mediators of cell signalling events, but also are recipients of signalling inputs from G protein coupled receptors (GPCRs) and their associated second messenger pathways. The coupling of GPCRs to calcium channels is optimized through the formation of receptor-channel complexes. In addition, this provides a mechanism for receptorchannel co-trafficking to and from the plasma membrane. On the other hand, voltage-gated calcium channel activity affects other types of ion channels such as voltage-and calcium-activated potassium channels. Coupling efficiency between these two families of channels is also enhanced through the formation of channel-channel complexes. This review provides a concise overview of the current state of knowledge on the physical interactions between voltage-gated calcium channels and members of the GPCR family, and with other types of ion channels.

  1. Channel in Kasei

    NASA Technical Reports Server (NTRS)

    2004-01-01

    14 November 2004 The Kasei Valles are a suite of very large, ancient outflow channels. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a portion of the youngest channel system in the Kasei Valles. Torrents of mud, rocks, and water carved this channel as flow was constricted through a narrow portion of the valley. Layers exposed by the erosion that created the channel can be seen in its walls. This 1.4 meters (5 feet) per pixel image is located near 21.1oN, 72.6oW. The picture covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

  2. Chondrocyte channel transcriptomics

    PubMed Central

    Lewis, Rebecca; May, Hannah; Mobasheri, Ali; Barrett-Jolley, Richard

    2013-01-01

    To date, a range of ion channels have been identified in chondrocytes using a number of different techniques, predominantly electrophysiological and/or biomolecular; each of these has its advantages and disadvantages. Here we aim to compare and contrast the data available from biophysical and microarray experiments. This letter analyses recent transcriptomics datasets from chondrocytes, accessible from the European Bioinformatics Institute (EBI). We discuss whether such bioinformatic analysis of microarray datasets can potentially accelerate identification and discovery of ion channels in chondrocytes. The ion channels which appear most frequently across these microarray datasets are discussed, along with their possible functions. We discuss whether functional or protein data exist which support the microarray data. A microarray experiment comparing gene expression in osteoarthritis and healthy cartilage is also discussed and we verify the differential expression of 2 of these genes, namely the genes encoding large calcium-activated potassium (BK) and aquaporin channels. PMID:23995703

  3. Proton channel models

    PubMed Central

    Pupo, Amaury; Baez-Nieto, David; Martínez, Agustín; Latorre, Ramón; González, Carlos

    2014-01-01

    Voltage-gated proton channels are integral membrane proteins with the capacity to permeate elementary particles in a voltage and pH dependent manner. These proteins have been found in several species and are involved in various physiological processes. Although their primary topology is known, lack of details regarding their structures in the open conformation has limited analyses toward a deeper understanding of the molecular determinants of their function and regulation. Consequently, the function-structure relationships have been inferred based on homology models. In the present work, we review the existing proton channel models, their assumptions, predictions and the experimental facts that support them. Modeling proton channels is not a trivial task due to the lack of a close homolog template. Hence, there are important differences between published models. This work attempts to critically review existing proton channel models toward the aim of contributing to a better understanding of the structural features of these proteins. PMID:24755912

  4. Calcium channel blocker overdose

    MedlinePlus

    ... Goldschlager N. Cardiovascular toxicology. In: Shannon MW, Borron SW, Burns MJ, eds. Haddad and Winchester's Clinical Management ... SD. Calcium channel antagonists. In: Shannon MW, Borron SW, Burns MJ, eds. Haddad and Winchester's Clinical Management ...

  5. TRP channels in disease.

    PubMed

    Jordt, S E; Ehrlich, B E

    2007-01-01

    The transient receptor potential (TRP) channels are a large family of proteins with six main subfamilies termed the TRPC (canonical), TRPV (vanilloid), TRPM (melastatin), TRPP (polycystin), TRPML (mucolipin), and TRPA (ankyrin) groups. The sheer number of different TRPs with distinct functions supports the statement that these channels are involved in a wide range of processes ranging from sensing of thermal and chemical signals to reloading intracellular stores after responding to an extracellular stimulus. Mutations in TRPs are linked to pathophysiology and specific diseases. An understanding of the role of TRPs in normal physiology is just beginning; the progression from mutations in TRPs to pathophysiology and disease will follow. In this review, we focus on two distinct aspects of TRP channel physiology, the role of TRP channels in intracellular Ca2+ homeostasis, and their role in the transduction of painful stimuli in sensory neurons. PMID:18193640

  6. A Simple Water Channel

    ERIC Educational Resources Information Center

    White, A. S.

    1976-01-01

    Describes a simple water channel, for use with an overhead projector. It is run from a water tap and may be used for flow visualization experiments, including the effect of streamlining and elementary building aerodynamics. (MLH)

  7. Intermittent communications modeling and simulation for autonomous unmanned maritime vehicles using an integrated APM and FSMC framework

    NASA Astrophysics Data System (ADS)

    Coker, Ayodeji; Straatemeier, Logan; Rogers, Ted; Valdez, Pierre; Griendling, Kelly; Cooksey, Daniel

    2014-06-01

    In this work a framework is presented for addressing the issue of intermittent communications faced by autonomous unmanned maritime vehicles operating at sea. In particular, this work considers the subject of predictive atmospheric signal transmission over multi-path fading channels in maritime environments. A Finite State Markov Channel is used to represent a Nakagami-m modeled physical fading radio channel. The range of the received signal-to-noise ratio is partitioned into a finite number of intervals which represent application-specific communications states. The Advanced Propagation Model (APM), developed at the Space and Naval Warfare Systems Center San Diego, provides a characterization of the transmission channel in terms of evaporation duct induced signal propagation loss. APM uses a hybrid ray-optic and parabolic equations model which allows for the computation of electromagnetic (EM) wave propagation over various sea and/or terrain paths. These models which have been integrated in the proposed framework provide a strategic and mission planning aid for the operation of maritime unmanned vehicles at sea.

  8. Ion Channels in Epithelial Cells

    NASA Astrophysics Data System (ADS)

    Palmer, Lawrence G.

    Ion channels in epithelial cells serve to move ions, and in some cases fluid, between compartments of the body. This function of the transfer of material is fundamentally different from that of the transfer of information, which is the main job of most channels in excitable cells. Nevertheless the basic construction of the channels is similar in many respects in the two tissue types. This chapter reviews the nature of channels in epithelia and discusses how their functions have evolved to accomplish the basic tasks for which they are responsible. I will focus on three channel types: epithelial Na+ channels, inward-rectifier K+ channels, and CFTR Cl- channels.

  9. Channel-tunnels.

    PubMed

    Koronakis, V; Andersen, C; Hughes, C

    2001-08-01

    TolC and its many homologues comprise an alpha-helical transperiplasmic tunnel embedded in the bacterial outer membrane by a contiguous beta-barrel channel, providing a large exit duct for diverse substrates. The 'channel-tunnel' is closed at its periplasmic entrance, but can be opened by an 'iris-like' mechanism when recruited by substrate-engaged proteins in the cytosolic membrane.

  10. Combined spatial diversity and time equalization for broadband multiple channel underwater acoustic communications

    NASA Astrophysics Data System (ADS)

    Skoro Kaskarovska, Violeta

    High data rate acoustic communications become feasible with the use of communication systems that operate at high frequency. The high frequency acoustic transmission in shallow water endures severe distortion as a result of the extensive intersymbol interference and Doppler shift, caused by the time variable multipath nature of the channel. In this research a Single Input Multiple Output (SIMO) acoustic communication system is developed to improve the reliability of the high data rate communications at short range in the shallow water acoustic channel. The proposed SIMO communication system operates at very high frequency and combines spatial diversity and decision feedback equalizer in a multilevel adaptive configuration. The first configuration performs selective combining on the equalized signals from multiple receivers and generates quality feedback parameter for the next level of combining. The second configuration implements a form of turbo equalization to evaluate the individual receivers using the feedback parameters as decision symbols. The improved signals from individual receivers are used in the next iteration of selective combining. Multiple iterations are used to achieve optimal estimate of the received signal. The multilevel adaptive configuration is evaluated on experimental and simulated data using SIMO system with three, four and five receivers. The simulation channel model developed for this research is based on experimental channel and Rician fading channel model. The performance of the channel is evaluated in terms of Bit Error Rate (BER) and Signal-to-Noise-and-Interference Ratio (SNIR). Using experimental data with non-zero BER, multilevel adaptive spatial diversity can achieve BER of 0 % and SNIR gain of 3 dB. The simulation results show that the average BER and SNIR after multilevel combining improve dramatically compared to the single receiver, even in case of extremely high BER of individual received signals. The results demonstrate the

  11. Morphodynamics of Floodplain Chute Channels

    NASA Astrophysics Data System (ADS)

    David, S. R.; Edmonds, D. A.

    2015-12-01

    Floodplain chute channel formation is a key process that can enable rivers to transition from single-thread to multi-thread planform geometries. Floodplain chute channels are usually incisional channels connecting topographic lows across point bars and in the floodplain. Surprisingly, it is still not clear what conditions promote chute channel formation and what governs their morphodynamic behavior. Towards this end we have initiated an empirical and theoretical study of floodplain chute channels in Indiana, USA. Using elevation models and satellite imagery we mapped 3064 km2 of floodplain in Indiana, and find that 37.3% of mapped floodplains in Indiana have extensive chute channel networks. These chute channel networks consist of two types of channel segments: meander cutoffs of the main channel and chute channels linking the cutoffs together. To understand how these chute channels link meander cutoffs together and eventually create floodplain channel networks we use Delft3D to explore floodplain morphodynamics. Our first modeling experiment starts from a generic floodplain prepopulated with meander cutoffs to test under what conditions chute channels form.We find that chute channel formation is optimized at an intermediate flood discharge. If the flood discharge is too large the meander cutoffs erosively diffuse, whereas if the floodwave is too small the cutoffs fill with sediment. A moderately sized floodwave reworks the sediment surrounding the topographic lows, enhancing the development of floodplain chute channels. Our second modeling experiments explore how floodplain chute channels evolve on the West Fork of the White River, Indiana, USA. We find that the floodplain chute channels are capable of conveying the entire 10 yr floodwave (Q=1330m3/s) leaving the inter-channel areas dry. Moreover, the chute channels can incise into the floodplain while the margins of channels are aggrading, creating levees. Our results suggest that under the right conditions

  12. Optical Communications Channel Combiner

    NASA Technical Reports Server (NTRS)

    Quirk, Kevin J.; Quirk, Kevin J.; Nguyen, Danh H.; Nguyen, Huy

    2012-01-01

    NASA has identified deep-space optical communications links as an integral part of a unified space communication network in order to provide data rates in excess of 100 Mb/s. The distances and limited power inherent in a deep-space optical downlink necessitate the use of photon-counting detectors and a power-efficient modulation such as pulse position modulation (PPM). For the output of each photodetector, whether from a separate telescope or a portion of the detection area, a communication receiver estimates a log-likelihood ratio for each PPM slot. To realize the full effective aperture of these receivers, their outputs must be combined prior to information decoding. A channel combiner was developed to synchronize the log-likelihood ratio (LLR) sequences of multiple receivers, and then combines these into a single LLR sequence for information decoding. The channel combiner synchronizes the LLR sequences of up to three receivers and then combines these into a single LLR sequence for output. The channel combiner has three channel inputs, each of which takes as input a sequence of four-bit LLRs for each PPM slot in a codeword via a XAUI 10 Gb/s quad optical fiber interface. The cross-correlation between the channels LLR time series are calculated and used to synchronize the sequences prior to combining. The output of the channel combiner is a sequence of four-bit LLRs for each PPM slot in a codeword via a XAUI 10 Gb/s quad optical fiber interface. The unit is controlled through a 1 Gb/s Ethernet UDP/IP interface. A deep-space optical communication link has not yet been demonstrated. This ground-station channel combiner was developed to demonstrate this capability and is unique in its ability to process such a signal.

  13. A review of radio channel models for body centric communications

    NASA Astrophysics Data System (ADS)

    Cotton, Simon L.; D'Errico, Raffaele; Oestges, Claude

    2014-06-01

    The human body is an extremely challenging environment for the operation of wireless communications systems, not least because of the complex antenna-body electromagnetic interaction effects which can occur. This is further compounded by the impact of movement and the propagation characteristics of the local environment which all have an effect upon body centric communications channels. As the successful design of body area networks (BANs) and other types of body centric system is inextricably linked to a thorough understanding of these factors, the aim of this paper is to conduct a survey of the current state of the art in relation to propagation and channel models primarily for BANs but also considering other types of body centric communications. We initially discuss some of the standardization efforts performed by the Institute of Electrical and Electronics Engineers 802.15.6 task group before focusing on the two most popular types of technologies currently being considered for BANs, namely narrowband and Ultrawideband (UWB) communications. For narrowband communications the applicability of a generic path loss model is contended, before presenting some of the scenario specific models which have proven successful. The impacts of human body shadowing and small-scale fading are also presented alongside some of the most recent research into the Doppler and time dependencies of BANs. For UWB BAN communications, we again consider the path loss as well as empirical tap delay line models developed from a number of extensive channel measurement campaigns conducted by research institutions around the world. Ongoing efforts within collaborative projects such as Committee on Science and Technology Action IC1004 are also described. Finally, recent years have also seen significant developments in other areas of body centric communications such as off-body and body-to-body communications. We highlight some of the newest relevant research in these areas as well as discussing

  14. A review of radio channel models for body centric communications

    PubMed Central

    Cotton, Simon L; D'Errico, Raffaele; Oestges, Claude

    2014-01-01

    The human body is an extremely challenging environment for the operation of wireless communications systems, not least because of the complex antenna-body electromagnetic interaction effects which can occur. This is further compounded by the impact of movement and the propagation characteristics of the local environment which all have an effect upon body centric communications channels. As the successful design of body area networks (BANs) and other types of body centric system is inextricably linked to a thorough understanding of these factors, the aim of this paper is to conduct a survey of the current state of the art in relation to propagation and channel models primarily for BANs but also considering other types of body centric communications. We initially discuss some of the standardization efforts performed by the Institute of Electrical and Electronics Engineers 802.15.6 task group before focusing on the two most popular types of technologies currently being considered for BANs, namely narrowband and Ultrawideband (UWB) communications. For narrowband communications the applicability of a generic path loss model is contended, before presenting some of the scenario specific models which have proven successful. The impacts of human body shadowing and small-scale fading are also presented alongside some of the most recent research into the Doppler and time dependencies of BANs. For UWB BAN communications, we again consider the path loss as well as empirical tap delay line models developed from a number of extensive channel measurement campaigns conducted by research institutions around the world. Ongoing efforts within collaborative projects such as Committee on Science and Technology Action IC1004 are also described. Finally, recent years have also seen significant developments in other areas of body centric communications such as off-body and body-to-body communications. We highlight some of the newest relevant research in these areas as well as discussing

  15. Organellar Channels and Transporters

    PubMed Central

    Xu, Haoxing; Martinoia, Enrico; Szabo, Ildiko

    2015-01-01

    Decades of intensive research has led to the discovery of most plasma membrane ion channels and transporters and the characterization of their physiological functions. In contrast, although over 80% of transport processes occur inside the cells, the ion flux mechanisms across intracellular membranes (the endoplasmic reticulum, Golgi apparatus, endosomes, lysosomes, mitochondria, chloroplasts, and vacuoles) are difficult to investigate and remain poorly understood. Recent technical advances in super-resolution microscopy, organellar electrophysiology, organelle-targeted fluorescence imaging, and organelle proteomics have pushed a large step forward in the research of intracellular ion transport. Many new organellar channels are molecularly identified and electrophysiologically characterized. Additionally, molecular identification of many of these ion channels/transporters has made it possible to study their physiological functions by genetic and pharmacological means. For example, organellar channels have been shown to regulate important cellular processes such as programmed cell death and photosynthesis, and are involved in many different pathologies. This Special Issue (SI) on Organellar Channels and Transporters aims to provide a forum to discuss the recent advances and to define the standard and open questions in this exciting and rapidly-developing field. Along this line, a new Gordon Research Conference dedicated to the multidisciplinary study of intracellular membrane transport proteins will be launched this coming summer. PMID:25795199

  16. TRP Channels and Analgesia

    PubMed Central

    Premkumar, Louis S.; Abooj, Mruvil

    2013-01-01

    Since cloning and characterizing the first nociceptive ion channel Transient Receptor Potential (TRP) Vanilloid 1 (TRPV1), other TRP channels involved in nociception have been cloned and characterized, which include TRP Vanilloid 2 (TRPV2), TRP Vanilloid 3 (TRPV3), TRP Vanilloid 4 (TRPV4), TRP Ankyrin 1 (TRPA1) and TRP Melastatin 8 (TRPM8), more recently TRP Canonical 1, 5, 6 (TRPC1, 5, 6), TRP Melastatin 2 (TRPM2) and TRP Melastatin 3 (TRPM3). These channels are predominantly expressed in C and Aδ nociceptors and transmit noxious thermal, mechanical and chemical sensitivities. TRP channels are modulated by pro-inflammatory mediators, neuropeptides and cytokines. Significant advances have been made targeting these receptors either by antagonists or agonists to treat painful conditions. In this review, we will discuss TRP channels as targets for next generation analgesics and the side effects that may ensue as a result of blocking/activating these receptors, because they are also involved in physiological functions such as release of vasoactive neuropeptides and regulation of vascular tone, maintenance of the body temperature, gastrointestinal motility, urinary bladder control etc. PMID:22910182

  17. MEMS in microfluidic channels.

    SciTech Connect

    Ashby, Carol Iris Hill; Okandan, Murat; Michalske, Terry A.; Sounart, Thomas L.; Matzke, Carolyn M.

    2004-03-01

    Microelectromechanical systems (MEMS) comprise a new class of devices that include various forms of sensors and actuators. Recent studies have shown that microscale cantilever structures are able to detect a wide range of chemicals, biomolecules or even single bacterial cells. In this approach, cantilever deflection replaces optical fluorescence detection thereby eliminating complex chemical tagging steps that are difficult to achieve with chip-based architectures. A key challenge to utilizing this new detection scheme is the incorporation of functionalized MEMS structures within complex microfluidic channel architectures. The ability to accomplish this integration is currently limited by the processing approaches used to seal lids on pre-etched microfluidic channels. This report describes Sandia's first construction of MEMS instrumented microfluidic chips, which were fabricated by combining our leading capabilities in MEMS processing with our low-temperature photolithographic method for fabricating microfluidic channels. We have explored in-situ cantilevers and other similar passive MEMS devices as a new approach to directly sense fluid transport, and have successfully monitored local flow rates and viscosities within microfluidic channels. Actuated MEMS structures have also been incorporated into microfluidic channels, and the electrical requirements for actuation in liquids have been quantified with an elegant theory. Electrostatic actuation in water has been accomplished, and a novel technique for monitoring local electrical conductivities has been invented.

  18. Channel Identification Machines

    PubMed Central

    Lazar, Aurel A.; Slutskiy, Yevgeniy B.

    2012-01-01

    We present a formal methodology for identifying a channel in a system consisting of a communication channel in cascade with an asynchronous sampler. The channel is modeled as a multidimensional filter, while models of asynchronous samplers are taken from neuroscience and communications and include integrate-and-fire neurons, asynchronous sigma/delta modulators and general oscillators in cascade with zero-crossing detectors. We devise channel identification algorithms that recover a projection of the filter(s) onto a space of input signals loss-free for both scalar and vector-valued test signals. The test signals are modeled as elements of a reproducing kernel Hilbert space (RKHS) with a Dirichlet kernel. Under appropriate limiting conditions on the bandwidth and the order of the test signal space, the filter projection converges to the impulse response of the filter. We show that our results hold for a wide class of RKHSs, including the space of finite-energy bandlimited signals. We also extend our channel identification results to noisy circuits. PMID:23227035

  19. A stochastic mathematical model of the within-herd transmission dynamics of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV): fade-out and persistence.

    PubMed

    Evans, C M; Medley, G F; Creasey, S J; Green, L E

    2010-03-01

    A stochastic, mathematical model of a farrow-finish pig herd was developed and used to investigate the within-herd transmission dynamics of PRRSV, and to examine patterns of on-farm persistence and fade-out. The model was structured to represent the management of a typical European pig herd. Three parameters determining the natural history of infection were derived from the literature. Transmission parameters were chosen using PRRSV antibody data from a cross-sectional study of 103 pig herds (Evans et al., 2008). The seroprevalence by age was generated from the model at 21-day intervals and was compared to the cross-sectional field data using log-likelihood, accounting for the accuracy of the ELISA test used. The model was run for various isolation practices of purchased gilts, contact structure, herd size and the frequency of re-introduction of infectious gilts. The time-dependent log-likelihood patterns varied between herds in a similar way to patterns observed from serological values from the 103 farms. Essentially they indicated two patterns of seroprevalence: herds in which PRRSV was stably persistent, and herds in which PRRSV was unstable, either recently introduced or recently faded-out. With a herd size of 327 sows with identical management, fade-out of virus occurred within 4 weeks in 21.9% of simulations. Without isolation of gilts from sows, fade-out within 250 days decreased from 81.6% to 14.3% and for herd sizes of 75, 150, 300 and 600, the probability of persistence of virus for >1200 days was 4%, 13.4%, 20.4% and 18.2%, respectively. Introduction of virus at a rate of approximately 0.37 times per year resulted in virus persisting for >1200 days in 32.4% of simulations, compared with 17.6% for no re-introduction. Fade-out of virus was most likely to occur within breeding females before virus reached young stock. Persistence was more likely once PRRSV was present in piglets which in turn infected rearing-pigs. The probability of persistence was higher

  20. HST Imaging of Fading AGN Candidates. I. Host-galaxy Properties and Origin of the Extended Gas

    NASA Astrophysics Data System (ADS)

    Keel, William C.; Maksym, W. Peter; Bennert, Vardha N.; Lintott, Chris J.; Chojnowski, S. Drew; Moiseev, Alexei; Smirnova, Aleksandrina; Schawinski, Kevin; Urry, C. Megan; Evans, Daniel A.; Pancoast, Anna; Scott, Bryan; Showley, Charles; Flatland, Kelsi

    2015-05-01

    We present narrow- and medium-band Hubble Space Telescope imaging, with additional supporting ground-based imaging, spectrophotometry, and Fabry-Perot interferometric data, for eight galaxies identified as hosting a fading active galactic nucleus (AGN). These are selected to have AGN-ionized gas projected \\gt 10 kpc from the nucleus and energy budgets with a significant shortfall of ionizing radiation between the requirement to ionize the distant gas and the AGN as observed directly, indicating fading of the AGN on ≈50,000 yr timescales. This paper focuses on the host-galaxy properties and origin of the gas. In every galaxy, we identify evidence of ongoing or past interactions, including tidal tails, shells, and warped or chaotic dust structures; a similarly selected sample of obscured AGNs with extended ionized clouds shares this high incidence of disturbed morphologies. Several systems show multiple dust lanes in different orientations, broadly fit by differentially precessing disks of accreted material viewed ˜1.5 Gyr after its initial arrival. The host systems are of early Hubble type; most show nearly pure de Vaucouleurs surface brightness profiles and Sérsic indices appropriate for classical bulges, with one S0 and one SB0 galaxy. The gas has a systematically lower metallicity than the nuclei; three systems have abundances uniformly well below solar, consistent with an origin in tidally disrupted low-luminosity galaxies, while some systems have more nearly solar abundances (accompanied by such signatures as multiple Doppler components), which may suggest redistribution of gas by outflows within the host galaxies themselves. These aspects are consistent with a tidal origin for the extended gas in most systems, although the ionized gas and stellar tidal features do not always match closely. Unlike extended emission regions around many radio-loud AGNs, these clouds are kinematically dominated by rotation, in some cases in warped disks. Outflows can play

  1. Dequantization Via Quantum Channels

    NASA Astrophysics Data System (ADS)

    Andersson, Andreas

    2016-08-01

    For a unital completely positive map {Φ} ("quantum channel") governing the time propagation of a quantum system, the Stinespring representation gives an enlarged system evolving unitarily. We argue that the Stinespring representations of each power {Φ^m} of the single map together encode the structure of the original quantum channel and provide an interaction-dependent model for the bath. The same bath model gives a "classical limit" at infinite time {mto∞} in the form of a noncommutative "manifold" determined by the channel. In this way, a simplified analysis of the system can be performed by making the large-m approximation. These constructions are based on a noncommutative generalization of Berezin quantization. The latter is shown to involve very fundamental aspects of quantum-information theory, which are thereby put in a completely new light.

  2. Chaos in quantum channels

    NASA Astrophysics Data System (ADS)

    Hosur, Pavan; Qi, Xiao-Liang; Roberts, Daniel A.; Yoshida, Beni

    2016-02-01

    We study chaos and scrambling in unitary channels by considering their entanglement properties as states. Using out-of-time-order correlation functions to diagnose chaos, we characterize the ability of a channel to process quantum information. We show that the generic decay of such correlators implies that any input subsystem must have near vanishing mutual information with almost all partitions of the output. Additionally, we propose the negativity of the tripartite information of the channel as a general diagnostic of scrambling. This measures the delocalization of information and is closely related to the decay of out-of-time-order correlators. We back up our results with numerics in two non-integrable models and analytic results in a perfect tensor network model of chaotic time evolution. These results show that the butterfly effect in quantum systems implies the information-theoretic definition of scrambling.

  3. Chaos in quantum channels

    DOE PAGES

    Hosur, Pavan; Qi, Xiao-Liang; Roberts, Daniel A.; Yoshida, Beni

    2016-02-01

    For this research, we study chaos and scrambling in unitary channels by considering their entanglement properties as states. Using out-of-time-order correlation functions to diagnose chaos, we characterize the ability of a channel to process quantum information. We show that the generic decay of such correlators implies that any input subsystem must have near vanishing mutual information with almost all partitions of the output. Additionally, we propose the negativity of the tripartite information of the channel as a general diagnostic of scrambling. This measures the delocalization of information and is closely related to the decay of out-of-time-order correlators. We back upmore » our results with numerics in two non-integrable models and analytic results in a perfect tensor network model of chaotic time evolution. In conclusion, these results show that the butterfly effect in quantum systems implies the information-theoretic definition of scrambling.« less

  4. Dequantization Via Quantum Channels

    NASA Astrophysics Data System (ADS)

    Andersson, Andreas

    2016-10-01

    For a unital completely positive map {Φ} ("quantum channel") governing the time propagation of a quantum system, the Stinespring representation gives an enlarged system evolving unitarily. We argue that the Stinespring representations of each power {Φ^m} of the single map together encode the structure of the original quantum channel and provide an interaction-dependent model for the bath. The same bath model gives a "classical limit" at infinite time {mto∞} in the form of a noncommutative "manifold" determined by the channel. In this way, a simplified analysis of the system can be performed by making the large- m approximation. These constructions are based on a noncommutative generalization of Berezin quantization. The latter is shown to involve very fundamental aspects of quantum-information theory, which are thereby put in a completely new light.

  5. Entanglement-saving channels

    NASA Astrophysics Data System (ADS)

    Lami, L.; Giovannetti, V.

    2016-03-01

    The set of Entanglement Saving (ES) quantum channels is introduced and characterized. These are completely positive, trace preserving transformations which when acting locally on a bipartite quantum system initially prepared into a maximally entangled configuration, preserve its entanglement even when applied an arbitrary number of times. In other words, a quantum channel ψ is said to be ES if its powers ψn are not entanglement-breaking for all integers n. We also characterize the properties of the Asymptotic Entanglement Saving (AES) maps. These form a proper subset of the ES channels that is constituted by those maps that not only preserve entanglement for all finite n but which also sustain an explicitly not null level of entanglement in the asymptotic limit n → ∞. Structure theorems are provided for ES and for AES maps which yield an almost complete characterization of the former and a full characterization of the latter.

  6. Channel plate for DNA sequencing

    DOEpatents

    Douthart, R.J.; Crowell, S.L.

    1998-01-13

    This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface. 15 figs.

  7. Channel plate for DNA sequencing

    DOEpatents

    Douthart, Richard J.; Crowell, Shannon L.

    1998-01-01

    This invention is a channel plate that facilitates data compaction in DNA sequencing. The channel plate has a length, a width and a thickness, and further has a plurality of channels that are parallel. Each channel has a depth partially through the thickness of the channel plate. Additionally an interface edge permits electrical communication across an interface through a buffer to a deposition membrane surface.

  8. Sodium channels and pain.

    PubMed

    Habib, Abdella M; Wood, John N; Cox, James J

    2015-01-01

    Human and mouse genetic studies have led to significant advances in our understanding of the role of voltage-gated sodium channels in pain pathways. In this chapter, we focus on Nav1.7, Nav1.8, Nav1.9 and Nav1.3 and describe the insights gained from the detailed analyses of global and conditional transgenic Nav knockout mice in terms of pain behaviour. The spectrum of human disorders caused by mutations in these channels is also outlined, concluding with a summary of recent progress in the development of selective Nav1.7 inhibitors for the treatment of pain. PMID:25846613

  9. Zeolites: Exploring Molecular Channels

    SciTech Connect

    Arslan, Ilke; Derewinski, Mirek

    2015-05-22

    Synthetic zeolites contain microscopic channels, sort of like a sponge. They have many uses, such as helping laundry detergent lather, absorbing liquid in kitty litter, and as catalysts to produce fuel. Of the hundreds of types of zeolites, only about 15 are used for catalysis. PNNL catalysis scientists Ilke Arslan and Mirek Derewinksi are studying these zeolites to understand what make them special. By exploring the mystery of these microscopic channels, their fundamental findings will help design better catalysts for applications such as biofuel production.

  10. Compilation and Analysis of 20- and 30-GHz Rain Fade Events at the ACTS NASA Ground Station: Statistics and Model Assessment

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1995-01-01

    Since the beginning of the operational phase of the NASA Research Center's Advanced Communication Technology Satellite (ACTS), signal-fade measurements have been recorded at the NASA Ground Station located in Cleveland, Ohio, with the use of the 20- and 30-GHz beacon signals. Compilations of the daily data have been statistically analyzed on a monthly and yearly basis. Such analyses have yielded relevant parameters as (1) cumulative monthly and yearly probability distributions of signal attenuation by rain, (2) attenuation duration versus attenuation threshold probabilities, and (3) rate-of-fade probabilities. Not only are such data needed for a realistic data base to support the design and performance analysis of future satellite systems, but they are necessary to assess predictions made with the ACTS Rain Attenuation Prediction Model.

  11. Channels of Propaganda.

    ERIC Educational Resources Information Center

    Sproule, J. Michael

    Defining propaganda as "efforts by special interests to win over the public covertly by infiltrating messages into various channels of public expression ordinarily viewed as politically neutral," this book argues that propaganda has become pervasive in American life. Pointing out that the 1990s society is inundated with propaganda from numerous…

  12. Learning in Tactile Channels

    ERIC Educational Resources Information Center

    Gescheider, George A.; Wright, John H.

    2012-01-01

    Vibrotactile intensity-discrimination thresholds for sinusoidal stimuli applied to the thenar eminence of the hand declined as a function of practice. However, improvement was confined to the tactile information-processing channel in which learning had occurred. Specifically, improvements in performance with training within the Pacinian-corpuscle…

  13. SK channels and calmodulin.

    PubMed

    Adelman, John P

    2016-01-01

    Calcium ions are Nature's most widely used signaling mechanism, mediating communication between pathways at virtually every physiological level. Ion channels are no exception, as the activities of a wide range of ion channels are intricately shaped by fluctuations in intracellular Ca(2+) levels. Mirroring the importance and the breadth of Ca(2+) signaling, free Ca(2+) levels are tightly controlled, and a myriad of Ca(2+) binding proteins transduce Ca(2+) signals, each with its own nuance, comprising a constantly changing symphony of metabolic activity. The founding member of Ca(2+) binding proteins is calmodulin (CaM), a small, acidic, modular protein endowed with gymnastic-like flexibility and E-F hand motifs that chelate Ca(2+) ions. In this review, I will trace the history that led to the realization that CaM serves as the Ca(2+)-gating cue for SK channels, the experiments that revealed that CaM is an intrinsic subunit of SK channels, and itself a target of regulation. PMID:25942650

  14. Chemistry in Microfluidic Channels

    ERIC Educational Resources Information Center

    Chia, Matthew C.; Sweeney, Christina M.; Odom, Teri W.

    2011-01-01

    General chemistry introduces principles such as acid-base chemistry, mixing, and precipitation that are usually demonstrated in bulk solutions. In this laboratory experiment, we describe how chemical reactions can be performed in a microfluidic channel to show advanced concepts such as laminar fluid flow and controlled precipitation. Three sets of…

  15. Developments in relativistic channeling

    SciTech Connect

    Carrigan, R.A. Jr.

    1996-10-01

    The possibility of using channeling as a tool for high energy accelerator applications and particle physics has now been extensively investigated. Bent crystals have been used for accelerator extraction and for particle deflection. Applications as accelerating devices have been discussed but have not yet been tried. 61 refs., 1 fig.

  16. Channeling through Bent Crystals

    SciTech Connect

    Mack, Stephanie; /Ottawa U. /SLAC

    2012-09-07

    Bent crystals have demonstrated potential for use in beam collimation. A process called channeling is when accelerated particle beams are trapped by the nuclear potentials in the atomic planes within a crystal lattice. If the crystal is bent then the particles can follow the bending angle of the crystal. There are several different effects that are observed when particles travel through a bent crystal including dechanneling, volume capture, volume reflection and channeling. With a crystal placed at the edge of a particle beam, part of the fringe of the beam can be deflected away towards a detector or beam dump, thus helping collimate the beam. There is currently FORTRAN code by Igor Yazynin that has been used to model the passage of particles through a bent crystal. Using this code, the effects mentioned were explored for beam energy that would be seen at the Facility for Advanced Accelerator Experimental Tests (FACET) at a range of crystal orientations with respect to the incoming beam. After propagating 5 meters in vacuum space past the crystal the channeled particles were observed to separate from most of the beam with some noise due to dechanneled particles. Progressively smaller bending radii, with corresponding shorter crystal lengths, were compared and it was seen that multiple scattering decreases with the length of the crystal therefore allowing for cleaner detection of the channeled particles. The input beam was then modified and only a portion of the beam sent through the crystal. With the majority of the beam not affected by the crystal, most particles were not deflected and after propagation the channeled particles were seen to be deflected approximately 5mm. After a portion of the beam travels through the crystal, the entire beam was then sent through a quadrupole magnet, which increased the separation of the channeled particles from the remainder of the beam to a distance of around 20mm. A different code, which was developed at SLAC, was used to

  17. A new insight on capacity fading of lithium-sulfur batteries: The effect of Li2S phase structure

    NASA Astrophysics Data System (ADS)

    Noh, Hyungjun; Song, Jongchan; Park, Jung-Ki; Kim, Hee-Tak

    2015-10-01

    In this work, a significant difference in Li2S phase structure, depending on the discharge rate, is reported for lithium sulfur (Li-S) batteries, and their performances are interpreted in terms of the phase structures. The production of crystalline Li2S is preferred at a low discharge rate, while the formation of amorphous Li2S is favored at a high discharge rate. The differences in the morphologies of the charged electrodes and the charging overvoltages demonstrate that the amorphous Li2S is more easily oxidized to soluble PS during charging compared to the crystalline Li2S. Impedance spectroscopic analysis reveals a faster Li ion diffusion through the amorphous Li2S discharge product is responsible for the smaller overvoltage and higher reversibility at the higher discharge rate. The slower capacity fade rate at a higher discharge rate indicates the importance of the Li2S phase structure on Li-S battery performances. The formation of amorphous Li2S is more favored with cycling, which provides a feasible explanation for widely observed capacity saturation behavior.

  18. The use of echocardiography in the critically ill; the role of FADE (Fast Assessment Diagnostic Echocardiography) training.

    PubMed

    Marum, Susan; Price, Susanna

    2011-08-01

    Echocardiography (echo) is a powerful technique that permits direct visualization and assessment of all the cardiac structures and assessment of the patients' haemodynamic status at the bedside. Echo allows detection of valvular disease, evaluation of ventricular function and the pericardium, detection of intracardiac/intrapulmonary shunts, and can be used to calculate flows and relative pressures between the cardiac chambers. This rapid point-of-care haemodynamic evaluation provides information to guide therapeutic interventions, including volume resuscitation, instigation of vasoactive therapy and/or referral for specialist cardiac/surgical intervention. Although there is abundant evidence in the cardiology literature regarding the use of echo, data in the critical care arena is less well defined, but emerging. The use of echo by intensive care doctors is likely to become routine, and therefore training for intensivists in this technique needs to be developed and supported. The Portuguese Working Group on Echocardiography has developed a skill-based program, FADE (Focused Assessment Diagnostic Echocardiography) in order to train clinicians in the use of bedside ultrasound as a diagnostic and monitoring tool for the critically ill.

  19. Structural evolution and the capacity fade mechanism upon long-term cycling in Li-rich cathode material.

    PubMed

    Song, Bohang; Liu, Zongwen; Lai, Man On; Lu, Li

    2012-10-01

    High capacity Li-rich layered cathode Li(Li(0.2)Mn(0.54)Ni(0.13)Co(0.13))O(2) and doped one are investigated to understand mechanisms of capacity fade as well as voltage decrease upon long-term cycling. Detailed electrochemical analysis reveals a phase-separation-like behavior with increase in the cycle number, which is responsible for gradual reduction in discharge voltage. X-ray photoelectron spectroscopy (XPS), transmission electron microscope coupled with energy dispersive X-ray spectroscopy (TEM-EDS) and inductively coupled plasma emission spectrometry (ICP) analysis results show increase in valence of transition metals on the surface of powder at a fully discharged state in addition to surface dissolution of Ni, leading to rapid capacity loss. High resolution transmission electron microscopy (HR-TEM) shows a phase transformation from original layered structure into spinel-like nano-domains in local structure. Though such an unexpected structural change is unfavorable because of lower output voltage, it is observed to be beneficial for high-rate performance.

  20. [Administration of sugammadex to a patient with myasthenia gravis with fade of the train-of-four ratio].

    PubMed

    Sugawara, Ami; Sasakawa, Tomoki; Hasegawa, Naoyoshi; Takahata, Osamu; Iwasaki, Hiroshi

    2011-09-01

    A 50-year-old man (weight 87 kg, height 171 cm) with myasthenia gravis (MG) was scheduled for extended thymectomy under general anesthesia. His preanesthetic train-of-four ratio (T4/T1) was 59%. The first twitch of the train-of-four (T1) was 130% after calibration. We administered rocuronium 10 mg (0.11 mg x kg(-1)) for tracheal intubation. Maximal suppression was achieved in 50 seconds. During the operation, we did continuous infusion of rocuronium to maintain T1 at 10%. We discontinued rocuronium infusion before the end of surgery. In patients with MG, deep levels of neuromuscular block can be achieved with less rocuronium. We hypothesized that the requirement of sugammadex in a patient with MG is less than that in normal patients. Therefore, we administered 0.5 mg x kg(-1) of sugammadex. After 5 min, T4/T1 had reached 54%, but T1 had not reached the control value; therefore, we administered additional 1.5 m x kg(-1) of sugammadex. Subsequently, T1 reached 120%. Patients with MG with fade on T4/T1 require a full dose of sugammadex, identical to the dose administered to normal patients.

  1. Capacity fading mechanism during long-term cycling of over-discharged LiCoO2/mesocarbon microbeads battery

    NASA Astrophysics Data System (ADS)

    Zhang, Lingling; Ma, Yulin; Cheng, Xinqun; Du, Chunyu; Guan, Ting; Cui, Yingzhi; Sun, Shun; Zuo, Pengjian; Gao, Yunzhi; Yin, Geping

    2015-10-01

    The LiCoO2/mesocarbon microbeads (MCMB) batteries are over-discharged to 102% DOD, 105% DOD and 115% DOD, respectively, then are fully charged and cycled 1000 times at 0.6 C with 30% DOD. The capacity fading mechanism during long-term cycling of over-discharged batteries is analyzed by electrochemical and physical characterization. No remarkable difference is found on the morphology of LiCoO2 material from SEM. However, copper is detected on anode over-discharged to 115% DOD by EDS and XRD. The structures of LiCoO2 and MCMB materials have almost no change according to the result of XRD test. The performance of MCMB material can be degraded by over-discharge, however the LiCoO2 material still keeps good performance. The capacity of MCMB electrode is improved after being washed with water to remove the SEI film, indicating that the capacity loss of MCMB electrode is mainly attributed to the increase of SEI film. The capacity deterioration of over-discharged battery is mainly caused by the dissolution of copper current collector and the deposition of Cu on the surface of anode during the following charging process. The copper deposited on the surface of anode can hinder the lithium intercalation into/de-intercalation from the anode and promote the increase of SEI film.

  2. Performance Evaluation of Localization Accuracy for a Log-Normal Shadow Fading Wireless Sensor Network under Physical Barrier Attacks.

    PubMed

    Hussein, Ahmed Abdulqader; Rahman, Tharek A; Leow, Chee Yen

    2015-01-01

    Localization is an apparent aspect of a wireless sensor network, which is the focus of much interesting research. One of the severe conditions that needs to be taken into consideration is localizing a mobile target through a dispersed sensor network in the presence of physical barrier attacks. These attacks confuse the localization process and cause location estimation errors. Range-based methods, like the received signal strength indication (RSSI), face the major influence of this kind of attack. This paper proposes a solution based on a combination of multi-frequency multi-power localization (C-MFMPL) and step function multi-frequency multi-power localization (SF-MFMPL), including the fingerprint matching technique and lateration, to provide a robust and accurate localization technique. In addition, this paper proposes a grid coloring algorithm to detect the signal hole map in the network, which refers to the attack-prone regions, in order to carry out corrective actions. The simulation results show the enhancement and robustness of RSS localization performance in the face of log normal shadow fading effects, besides the presence of physical barrier attacks, through detecting, filtering and eliminating the effect of these attacks. PMID:26690159

  3. Structures responsible for rapid fading of medium frequency radio reflections from the day-time E-layer

    NASA Astrophysics Data System (ADS)

    Jones, K. L.

    1984-12-01

    The steerable beam Bribie Island radar (152 deg E, 27 deg S) operating at a frequency of 1.98 MHz was used to obtain data relevant to reflection conditions near 100 km altitude on 7 days during June-October 1982. The rapid signal fading commonly observed is primarily due to transient reflectors with lifetimes of a few seconds, often seen up to angles of 20 deg from the zenith. Longer lived moving reflectors (presumed to be sporadic-E clouds) also play a part. Certain properties of the transient reflectors are consistent with a turbulent generation mechanism. However, any theory of their origin must explain why, for about a third of the time, they tend to occur preferentially to the north and east of the observing site. A direct comparison of velocities using Doppler and spaced antenna drifts methods shows reasonable agreement when the data is averaged over quarter hour periods. However, conclusions by previous workers, on the basis of observations of motions of diffraction patterns, that the ionospheric structure responsible for the diffraction pattern observed on the ground is undulations of the isoionic contours by gravity waves, is not supported by a detailed analysis of the data.

  4. Evaluation of the sensitivity and fading characteristics of an image plate system for x-ray diagnostics

    NASA Astrophysics Data System (ADS)

    Meadowcroft, A. L.; Bentley, C. D.; Stott, E. N.

    2008-11-01

    Image plates (IPs) are a reusable recording media capable of detecting ionizing radiation, used to diagnose x-ray emission from laser-plasma experiments. Due to their superior performance characteristics in x-ray applications [C. C. Bradford, W. W. Peppler, and J. T. Dobbins III, Med. Phys. 26, 27 (1999) and J. Digit. Imaging. 12, 54 (1999)], the Fuji Biological Analysis System (BAS) IPs are fielded on x-ray diagnostics for the HELEN laser by the Plasma Physics Department at AWE. The sensitivities of the Fuji BAS IPs have been absolutely calibrated for absolute measurements of x-ray intensity in the energy range of 0-100 keV. In addition, the Fuji BAS IP fading as a function of time was investigated. We report on the characterization of three Fuji BAS IP responses to x-rays using a radioactive source, and discrete x-ray line energies generated by the Excalibur soft x-ray facility and the Defense Radiological Standards Centre filter-fluorescer hard x-ray system at AWE.

  5. Performance Evaluation of Localization Accuracy for a Log-Normal Shadow Fading Wireless Sensor Network under Physical Barrier Attacks

    PubMed Central

    Abdulqader Hussein, Ahmed; Rahman, Tharek A.; Leow, Chee Yen

    2015-01-01

    Localization is an apparent aspect of a wireless sensor network, which is the focus of much interesting research. One of the severe conditions that needs to be taken into consideration is localizing a mobile target through a dispersed sensor network in the presence of physical barrier attacks. These attacks confuse the localization process and cause location estimation errors. Range-based methods, like the received signal strength indication (RSSI), face the major influence of this kind of attack. This paper proposes a solution based on a combination of multi-frequency multi-power localization (C-MFMPL) and step function multi-frequency multi-power localization (SF-MFMPL), including the fingerprint matching technique and lateration, to provide a robust and accurate localization technique. In addition, this paper proposes a grid coloring algorithm to detect the signal hole map in the network, which refers to the attack-prone regions, in order to carry out corrective actions. The simulation results show the enhancement and robustness of RSS localization performance in the face of log normal shadow fading effects, besides the presence of physical barrier attacks, through detecting, filtering and eliminating the effect of these attacks. PMID:26690159

  6. Thermoluminescence (TL) Analysis and Fading Studies of Naturally Occurring Salt Irradiated by 500 mGy Gamma Rays

    SciTech Connect

    Tiwari, Ramesh Chandra; Pau, Kham Suan

    2011-10-20

    The aim of the present study was to investigate the potential of the naturally occurring salt for the dosimetry purposes, using TL. The fine powder samples (20 mg) were irradiated by {gamma}- rays from 500 mGy to 2500 mGy by using Theratron-780C Cobalt-60 source, however, this paper discusses about 500 mGy only. The TL glow curve peak parameters were studied by using Chen's peak shape equation. TL glow curves were compared with fitted curves using glow curve deconvolution (GCD) method by using Kitis expression. The kinetic parameter values (E, b and s) so calculated, are in good agreement with those available in literature. The calculated energy values were also verified by using various heating rate (VHR) method. {chi}{sup 2} test and figure of merit (FOM) calculation was done to accept the goodness of fit between the curves. Fading studies of the sample showed a good fitting between the curves. The analysis suggests that natural salt should be considered for dosimetry purposes.

  7. Fade statistics of a ground-to-satellite optical link in the presence of lead-ahead and aperture mismatch.

    PubMed

    Basu, Santasri; Voelz, David; Borah, Deva K

    2009-03-01

    In a recent publication [J. Opt. Soc. Am. A25, 1594-1608 (2008).JOAOD60740-323210.1364/JOSAA.25.001594] we developed expressions for the tilt errors that arise from the effects of lead-ahead and aperture mismatch when transmitting a laser beam from the ground to a satellite. We extend these results to examine the fade statistics of the irradiance at the satellite due to these tilt errors and turbulence induced scintillation. The system concept is that the light from a beacon on the satellite is received by the ground station and a derived signal is used to drive a tracking/pointing system for the uplink beam. However, the beam must be pointed ahead along the satellite track to intercept the satellite (lead-ahead), and physical constraints may require that the beam transmit aperture is different in size or location than the aperture receiving the beacon signal (aperture mismatch). These two issues cause the light entering the receiving aperture (tracker) and the beam exiting the transmit aperture (pointer) to traverse somewhat different turbulence volumes, which limits the ability of the tracking/pointing system to place the maximum flux on the satellite.

  8. Thermoluminescence (TL) Analysis and Fading Studies of Naturally Occurring Salt Irradiated by 500 mGy Gamma Rays

    NASA Astrophysics Data System (ADS)

    Tiwari, Ramesh Chandra; Pau, Kham Suan

    2011-10-01

    The aim of the present study was to investigate the potential of the naturally occurring salt for the dosimetry purposes, using TL. The fine powder samples (20 mg) were irradiated by γ- rays from 500 mGy to 2500 mGy by using Theratron-780C Cobalt-60 source, however, this paper discusses about 500 mGy only. The TL glow curve peak parameters were studied by using Chen's peak shape equation. TL glow curves were compared with fitted curves using glow curve deconvolution (GCD) method by using Kitis expression. The kinetic parameter values (E, b and s) so calculated, are in good agreement with those available in literature. The calculated energy values were also verified by using various heating rate (VHR) method. χ2 test and figure of merit (FOM) calculation was done to accept the goodness of fit between the curves. Fading studies of the sample showed a good fitting between the curves. The analysis suggests that natural salt should be considered for dosimetry purposes.

  9. Chip-interleaved optical code division multiple access relying on a photon-counting iterative successive interference canceller for free-space optical channels.

    PubMed

    Zhou, Xiaolin; Zheng, Xiaowei; Zhang, Rong; Hanzo, Lajos

    2013-07-01

    In this paper, we design a novel Poisson photon-counting based iterative successive interference cancellation (SIC) scheme for transmission over free-space optical (FSO) channels in the presence of both multiple access interference (MAI) as well as Gamma-Gamma atmospheric turbulence fading, shot-noise and background light. Our simulation results demonstrate that the proposed scheme exhibits a strong MAI suppression capability. Importantly, an order of magnitude of BER improvements may be achieved compared to the conventional chip-level optical code-division multiple-access (OCDMA) photon-counting detector.

  10. A photon-counting spatial-diversity-and-multiplexing MIMO scheme for Poisson atmospheric channels relying on Q-ary PPM.

    PubMed

    Zhou, Xiaolin; Zhang, Dingchen; Zhang, Rong; Hanzo, Lajos

    2012-11-19

    A novel Photon-Counting Spatial-Diversity-and-Multiplexing (PC-SDM) scheme is proposed for high-speed Free-Space Optical (FSO) transmission over shot-noise limited Poisson channels experiencing turbulence-induced fading. In particular, Iterative Parallel Interference Cancellation (Iter-PIC) aided Q-ary Pulse Position Modulation (Q-PPM) is employed. Simulation results demonstrate that our proposed scheme exhibits a high integrity and a high throughput, while mitigating the effects of multi-stream interference and background radiation noise.

  11. Average bit error rate performance analysis of subcarrier intensity modulated MRC and EGC FSO systems with dual branches over M distribution turbulence channels

    NASA Astrophysics Data System (ADS)

    Wang, Ran-ran; Wang, Ping; Cao, Tian; Guo, Li-xin; Yang, Yintang

    2015-07-01

    Based on the space diversity reception, the binary phase-shift keying (BPSK) modulated free space optical (FSO) system over Málaga (M) fading channels is investigated in detail. Under independently and identically distributed and independently and non-identically distributed dual branches, the analytical average bit error rate (ABER) expressions in terms of H-Fox function for maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques are derived, respectively, by transforming the modified Bessel function of the second kind into the integral form of Meijer G-function. Monte Carlo (MC) simulation is also provided to verify the accuracy of the presented models.

  12. Shrinking the FadE proteome of Mycobacterium tuberculosis: insights into cholesterol metabolism through identification of an α2β2 heterotetrameric acyl coenzyme A dehydrogenase family.

    PubMed

    Wipperman, Matthew F; Yang, Meng; Thomas, Suzanne T; Sampson, Nicole S

    2013-10-01

    The ability of the pathogen Mycobacterium tuberculosis to metabolize steroids like cholesterol and the roles that these compounds play in the virulence and pathogenesis of this organism are increasingly evident. Here, we demonstrate through experiments and bioinformatic analysis the existence of an architecturally distinct subfamily of acyl coenzyme A (acyl-CoA) dehydrogenase (ACAD) enzymes that are α2β2 heterotetramers with two active sites. These enzymes are encoded by two adjacent ACAD (fadE) genes that are regulated by cholesterol. FadE26-FadE27 catalyzes the dehydrogenation of 3β-hydroxy-chol-5-en-24-oyl-CoA, an analog of the 5-carbon side chain cholesterol degradation intermediate. Genes encoding the α2β2 heterotetrameric ACAD structures are present in multiple regions of the M. tuberculosis genome, and subsets of these genes are regulated by four different transcriptional repressors or activators: KstR1 (also known as KstR), KstR2, Mce3R, and SigE. Homologous ACAD gene pairs are found in other Actinobacteria, as well as Proteobacteria. Their structures and genomic locations suggest that the α2β2 heterotetrameric structural motif has evolved to enable catalysis of dehydrogenation of steroid- or polycyclic-CoA substrates and that they function in four subpathways of cholesterol metabolism.

  13. Extended X-ray emission in the IC 2497 - Hanny's Voorwerp system: energy injection in the gas around a fading AGN

    NASA Astrophysics Data System (ADS)

    Sartori, Lia F.; Schawinski, Kevin; Koss, Michael; Treister, Ezequiel; Maksym, W. Peter; Keel, William C.; Urry, C. Megan; Lintott, Chris J.; Wong, O. Ivy

    2016-04-01

    We present deep Chandra X-ray observations of the core of IC 2497, the galaxy associated with Hanny's Voorwerp and hosting a fading AGN. We find extended soft X-ray emission from hot gas around the low intrinsic luminosity (unobscured) AGN (Lbol ˜ 1042-1044 erg s-1). The temperature structure in the hot gas suggests the presence of a bubble or cavity around the fading AGN ({{E}}_bub ˜ 10^{54}{-}10^{55} erg). A possible scenario is that this bubble is inflated by the fading AGN, which after changing accretion state is now in a kinetic mode. Other possibilities are that the bubble has been inflated by the past luminous quasar (Lbol ˜ 1046 erg s-1), or that the temperature gradient is an indication of a shock front from a superwind driven by the AGN. We discuss the possible scenarios and the implications for the AGN-host galaxy interaction, as well as an analogy between AGN and X-ray binaries lifecycles. We conclude that the AGN could inject mechanical energy into the host galaxy at the end of its lifecycle, and thus provide a source for mechanical feedback, in a similar way as observed for X-ray binaries.

  14. Shrinking the FadE Proteome of Mycobacterium tuberculosis: Insights into Cholesterol Metabolism through Identification of an α2β2 Heterotetrameric Acyl Coenzyme A Dehydrogenase Family

    PubMed Central

    Wipperman, Matthew F.; Yang, Meng; Thomas, Suzanne T.

    2013-01-01

    The ability of the pathogen Mycobacterium tuberculosis to metabolize steroids like cholesterol and the roles that these compounds play in the virulence and pathogenesis of this organism are increasingly evident. Here, we demonstrate through experiments and bioinformatic analysis the existence of an architecturally distinct subfamily of acyl coenzyme A (acyl-CoA) dehydrogenase (ACAD) enzymes that are α2β2 heterotetramers with two active sites. These enzymes are encoded by two adjacent ACAD (fadE) genes that are regulated by cholesterol. FadE26-FadE27 catalyzes the dehydrogenation of 3β-hydroxy-chol-5-en-24-oyl-CoA, an analog of the 5-carbon side chain cholesterol degradation intermediate. Genes encoding the α2β2 heterotetrameric ACAD structures are present in multiple regions of the M. tuberculosis genome, and subsets of these genes are regulated by four different transcriptional repressors or activators: KstR1 (also known as KstR), KstR2, Mce3R, and SigE. Homologous ACAD gene pairs are found in other Actinobacteria, as well as Proteobacteria. Their structures and genomic locations suggest that the α2β2 heterotetrameric structural motif has evolved to enable catalysis of dehydrogenation of steroid- or polycyclic-CoA substrates and that they function in four subpathways of cholesterol metabolism. PMID:23836861

  15. Understanding capacity fade in silicon based electrodes for lithium-ion batteries using three electrode cells and upper cut-off voltage studies

    NASA Astrophysics Data System (ADS)

    Beattie, Shane D.; Loveridge, M. J.; Lain, Michael J.; Ferrari, Stefania; Polzin, Bryant J.; Bhagat, Rohit; Dashwood, Richard

    2016-01-01

    Commercial Li-ion batteries are typically cycled between 3.0 and 4.2 V. These voltages limits are chosen based on the characteristics of the cathode (e.g. lithium cobalt oxide) and anode (e.g. graphite). When alternative anode/cathode chemistries are studied the same cut-off voltages are often, mistakenly, used. Silicon (Si) based anodes are widely studied as a high capacity alternative to graphite for Lithium-ion batteries. When silicon-based anodes are paired with high capacity cathodes (e.g. Lithium Nickel Cobalt Aluminium Oxide; NCA) the cell typically suffers from rapid capacity fade. The purpose of this communication is to understand how the choice of upper cut-off voltage affects cell performance in Si/NCA cells. A careful study of three-electrode cell data will show that capacity fade in Si/NCA cells is due to an ever-evolving silicon voltage profile that pushes the upper voltage at the cathode to >4.4 V (vs. Li/Li+). This behaviour initially improves cycle efficiency, due to liberation of new lithium, but ultimately reduces cycling efficiency, resulting in rapid capacity fade.

  16. ESR dosimetry of fossil enamel: some comments about measurement precision, long-term signal fading and dose-response curve fitting.

    PubMed

    Duval, M; Guilarte Moreno, V; Grün, R

    2013-12-01

    This work deals with the specific studies of three main sources of uncertainty in electron spin resonance (ESR) dosimetry/dating of fossil tooth enamel: (1) the precision of the ESR measurements, (2) the long-term signal fading the selection of the fitting function. They show a different influence on the equivalent dose (D(E)) estimates. Repeated ESR measurements were performed on 17 different samples: results show a mean coefficient of variation of the ESR intensities of 1.20 ± 0.23 %, inducing a mean relative variability of 3.05 ± 2.29 % in the D(E) values. ESR signal fading over 5 y was also observed: its magnitude seems to be quite sample dependant but is nevertheless especially important for the most irradiated aliquots. This fading has an apparent random effect on the D(E) estimates. Finally, the authors provide new insights and recommendations about the fitting of ESR dose-response curves of fossil enamel with a double saturating exponential (DSE) function. The potential of a new variation of the DSE was also explored. Results of this study also show that the choice of the fitting function is of major importance, maybe more than the other sources previously mentioned, in order to get accurate final D(E) values.

  17. Assessment of rain fade mitigation techniques in the EHF band on a Syracuse 3 20/44-GHz low elevation link

    NASA Astrophysics Data System (ADS)

    de Montera, L.; Barthès, L.; Mallet, C.; Golé, P.; Marsault, T.

    2010-01-01

    An Earth-to-satellite propagation experiment in the EHF band has been carried out within the framework of the Syracuse 3 program, which is a new generation French military SATCOM system. The originality of this experiment resides in the link's frequencies (20 GHz downlink and 44 GHz uplink) and its low elevation angle (17°). The first part of the article presents a statistical analysis of attenuation data providing the long-term statistics, frequency scaling ratios and fade durations. These results are compared to standard ITU models. The second part of the article is dedicated to the short-term forecasting of rain fade, useful for the implementation of Fade Mitigation Techniques (FMT). Firstly, the downlink attenuation is predicted based on a non-linear ARIMA-GARCH model. The prediction result is then separated into several physical components (gases, clouds and rain) that are scaled to the uplink frequency using specific frequency scaling factors. The performance of the model is assessed based on Syracuse 3 20/44-GHz data collected during a period of 1 year.

  18. The Fading Affect Bias shows healthy coping at the general level, but not the specific level for religious variables across religious and non-religious events.

    PubMed

    Gibbons, Jeffrey A; Hartzler, Jennifer K; Hartzler, Andrew W; Lee, Sherman A; Walker, W Richard

    2015-11-01

    The research on fading emotions has shown that unpleasant emotions fade more over time than pleasant emotions, which is a phenomenon referred to as the Fading Affect Bias (FAB). Based on the negative relation between the FAB and dysphoria (Walker, Skowronski, Gibbons, Vogl, & Thompson, 2003), some researchers have argued that the FAB is a healthy coping mechanism (Walker, Skowronski, & Thompson, 2003). As religious variables are related to positive emotions and emotional coping (e.g., Cohen, 2002; Pargament, Smith, Koenig, & Perez, 1998), we examined the FAB as a healthy coping mechanism at the general and specific levels of analysis in the context of religion. General healthy coping was supported by (1) FAB effects across both religious events (REs) and non-religious events (NREs) and (2) a positive relation for spirituality and the FAB. However, specific healthy coping was not supported by a small FAB for (1) REs at high levels of positive religious coping (PRC) for NREs, (2) NREs at low levels of PRC for NREs, and (3) purely REs relative to REs involving spirituality. Other implications are discussed.

  19. MIMO Free-Space Optical Communication Employing Subcarrier Intensity Modulation in Atmospheric Turbulence Channels

    NASA Astrophysics Data System (ADS)

    Ghassemlooy, Zabih; Popoola, Wasiu O.; Ahmadi, Vahid; Leitgeb, Erich

    In this paper, we analyse the error performance of transmitter/receiver array free-space optical (FSO) communication system employing binary phase shift keying (BPSK) subcarrier intensity modulation (SIM) in clear but turbulent atmospheric channel. Subcarrier modulation is employed to eliminate the need for adaptive threshold detector. Direct detection is employed at the receiver and each subcarrier is subsequently demodulated coherently. The effect of irradiance fading is mitigated with an array of lasers and photodetectors. The received signals are linearly combined using the optimal maximum ratio combining (MRC), the equal gain combining (EGC) and the selection combining (SelC). The bit error rate (BER) equations are derived considering additive white Gaussian noise and log normal intensity fluctuations. This work is part of the EU COST actions and EU projects.

  20. K/Ka-band channel characterization for mobile satellite systems

    NASA Technical Reports Server (NTRS)

    Pinck, Deborah S.; Rice, Michael D.

    1995-01-01

    Mobile satellite systems allow truly ubiquitous wireless communications to users anywhere and anytime. NASA's Advanced Communications Technology Satellite (ACTS) provides an ideal space-based platform for the measurement of K/Ka band propagation characteristics in a land mobile satellite application. Field tests conducted in Southern California during the first seven months of 1994 using JPL's ACTS Mobile Terminal (AMT) provided channel characterization data for the K/Ka-band link. A pilot tone was transmitted from a fixed station in Cleveland, Ohio through the satellite and downlinked at 20 GHz in the Southern California spot beam. The AMT was equipped with a narrow beam, high gain antenna which tracked the satellite in azimuth for a fixed elevation angle (46 degrees for this case). The field tests were conducted in three basic environments: clear line-of-sight (LOS) highways, lightly shadowed suburban, and heavily shadowed suburban. Preliminary results of these field tests indicate very little multipath for rural environments and for clear LOS links (as expected with a narrow beam antenna). Deep fades were experienced in shadowed areas, especially those where tree canopies covered the road.