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Sample records for fading nakagami channels

  1. Outage Capacity Analysis of TAS/MRC Systems over Arbitrary Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Hung, Chia-Chun; Chiang, Ching-Tai; Lin, Shyh-Neng; Wu, Rong-Ching

    A simple closed-form approximation for the outage capacity of Transmit Antenna Selection/Maximal-Ratio Combining (TAS/MRC) systems over independent and identically distributed (i.i.d) Nakagami-m fading channels is derived while the fading index is a positive integer. When the Nakagami-m fading index is not an integer, the approximate outage capacity is derived as a single infinite series of Gamma function. Computer simulations verify the accuracy of the approximate results.

  2. A subspace-based parameter estimation algorithm for Nakagami-m fading channels

    NASA Astrophysics Data System (ADS)

    Dianat, Sohail; Rao, Raghuveer

    2010-04-01

    Estimation of channel fading parameters is an important task in the design of communication links such as maximum ratio combining (MRC). The MRC weights are directly related to the fading channel coefficients. In this paper, we propose a subspace based parameter estimation algorithm for the estimation of the parameters of Nakagami-m fading channels in the presence of additive white Gaussian noise. Comparisons of our proposed approach are made with other techniques available in the literature. The performance of the algorithm with respect to the Cramer-Rao bound (CRB) is investigated. Computer simulation results for different signal to noise ratios (SNR) are presented.

  3. Performance Analysis of Amplify-and-Forward Relaying over Shadowed Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Cai, Chunxiao; Cai, Yueming; Yang, Weiwei

    2011-11-01

    In the paper, the closed-form approximation for outage probability and symbol error probability are presented for amplify-and-forward cooperative network over shadowed Nakagami-m Fading Channels. Our results are verified through comparison with Monte Carlo simulations. It shows that our theoretical results can provide good approximations to the numerical results.

  4. Precise SER Analysis and Performance Results of OSTBC MIMO-OFDM Systems over Uncorrelated Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Ahmad Ansari, Ejaz; Rajatheva, Nandana

    Although the topic of multiple-input multiple-output (MIMO) based orthogonal frequency division multiplexing (OFDM) over different fading channels is well investigated, its closed form symbol error rate (SER) expressions and performance results employing orthogonal space time block codes (OSTBCs) over uncorrelated frequency-selective Nakagami-m fading channels are still not available. The closed form expressions are extremely useful for evaluating system's performance without carrying out time consuming simulations. Similarly, the performance results are also quite beneficial for determining the system's performance in the sense that many practical wireless standards extensively employ MIMO-OFDM systems in conjunction with M-ary quadrature amplitude modulation (M-QAM) constellation. This paper thus, derives exact closed form expressions for the SER of M-ary Gray-coded one and two dimensional constellations when an OSTBC is employed and Nt transmit antennas are selected for transmission over frequency-selective Nakagami-m fading channels. For this purpose, first an exact closed-form of average SER expression of OSTBC based MIMO-OFDM system for M-ary phase shift keying (M-PSK) using traditional probability density function (PDF) approach is derived. We then compute exact closed form average SER expressions for M-ary pulse amplitude modulation (M-PAM) and M-QAM schemes by utilizing this generalized result. These expressions are valid over both frequency-flat and frequency-selective Nakagami-m fading MIMO channels and can easily be evaluated without using any numerical integration methods. We also show that average SER of MIMO-OFDM system using OSTBC in case of frequency-selective Rayleigh fading channels remains independent to the number of taps, L of that fading channel and the performance of the same system for two-tap un-correlated Rayleigh and Nakagami-m fading channels is better than that of the correlated one. Moreover, Monte Carlo simulation of MIMO-OFDM system

  5. Outage Probability of Interference-limited Switch and Stay Diversity System over Gamma Shadowed Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Djordjevic, Goran T.; Antic, Dragan

    2013-12-01

    In this paper, the outage performance of a dual-branch switch and stay combining (SSC) diversity receiver operating over composite multipath Nakagami-m fading/gamma shadowing channels in the presence of a co-channel interference is determined. For a single channel composite fading environment, we derive the new analytical expressions for the probability density function and cumulative distribution function of the instantaneous signal-to-interference (SIR) ratio that can be used as alternatives to the previously published results. In the case of non-identically distributed and power unbalanced SSC branches with arbitrary fading parameters, the outage performance is determined. The choice of optimal switching threshold in minimum outage probability sense is discussed. The results show the outage probability dependence on simultaneous effects of the SIR unbalancing, as well as multipath fading and shadowing severities. The analytical results are confirmed by Monte Carlo simulations.

  6. Accurate Bit-Error Rate Evaluation for TH-PPM Systems in Nakagami Fading Channels Using Moment Generating Functions

    NASA Astrophysics Data System (ADS)

    Liang, Bin; Gunawan, Erry; Law, Choi Look; Teh, Kah Chan

    Analytical expressions based on the Gauss-Chebyshev quadrature (GCQ) rule technique are derived to evaluate the bit-error rate (BER) for the time-hopping pulse position modulation (TH-PPM) ultra-wide band (UWB) systems under a Nakagami-m fading channel. The analyses are validated by the simulation results and adopted to assess the accuracy of the commonly used Gaussian approximation (GA) method. The influence of the fading severity on the BER performance of TH-PPM UWB system is investigated.

  7. 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.

  8. Performance Analysis of Error Probabilities for Arbitrary 2-D Signaling with I/Q Unbalances over Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Lee, Jaeyoon; Yoon, Dongweon; Park, Sang Kyu

    Recently, we provided closed-form expressions involving two-dimensional (2-D) joint Gaussian Q-function for the symbol error rate (SER) and bit error rate (BER) of an arbitrary 2-D signal with I/Q unbalances over an additive white Gaussian noise (AWGN) channel [1]. In this letter, we extend the expressions to Nakagami-m fading channels. Using Craig representation of the 2-D joint Gaussian Q-function, we derive an exact and general expression for the error probabilities of arbitrary 2-D signaling with I/Q phase and amplitude unbalances over Nakagami-m fading channels.

  9. Parallel Decentralized Network for the Detection of Unknown Signals Through Wireless Nakagami Fading Channels

    NASA Astrophysics Data System (ADS)

    El-Bahaie, Ebtehal H.; Al-Hussaini, Emad K.

    2010-12-01

    In this paper analytical and simulation results for the decentralized detection of unknown signals are introduced. Parallel sensor network scheme is assumed. Additive White Gaussian Noise (AWGN) and Nakagami fading are assumed in both links, that is, from the source to the decentralized local sensors and from the sensors to the fusion center. Furthermore, diversity employing Square Law Combining (SLC) or Square Law Selection (SLS) is considered at each sensor, for both independent and correlated branches. Appreciable improvements are obtained with the increase of the number of sensors and the diversity employment.

  10. Analytic Nakagami fading parameter estimation in dependent noise channel using copula

    NASA Astrophysics Data System (ADS)

    Gholizadeh, Mohammad Hossein; Amindavar, Hamidreza; Ritcey, James A.

    2013-12-01

    In this paper, the probability density function (PDF) estimation is introduced in the framework of estimating the Nakagami fading parameter. This approach provides an analytic procedure for finding the fading parameter. Using the copula theory, an accurate PDF estimate is obtained even when the desired signal is corrupted in a noisy environment. In the real world, the noise samples could be highly dependent on the main signal. Copula-based models are a general set of statistical models defined for any multivariate random variable. Thus, they depict the statistical behavior of a received signal including two dependent terms, representative of the desired signal and noise. Previous works in the Nakagami parameter determination have mainly examined estimation based on either a noiseless sample model or an independent trivial noisy one. In this paper, we consider a more comprehensive situation about the noise destruction and our investigation is done in low signal-to-noise ratios. The parametric bootstrap method approves the accuracy of the analytically estimated PDF, and simulation results show that the new estimator has superior performance over conventional estimators.

  11. Average Fade Duration of Dual Selection Diversity over Correlated Unbalanced Nakagami-m Fading Channels in the Presence of Cochannel Interference

    NASA Astrophysics Data System (ADS)

    Panajotović, Aleksandra; Sekulović, Nikola; Drača, Dragan; Stefanović, Mihajlo; Stefanović, Časlav

    2013-12-01

    A dual selection combining (SC) receiver with correlated and unbalanced diversity branches operating in interference-limited Nakagami-m fading environment is considered in this paper. Actually, average fade duration (AFD) of SC system applying desired signal decision algorithm is obtained. Numerical results can be used to examine the effects of fading severity, input signal-to-interference ratio (SIR) unbalance and level of branch correlation on the AFD, as well as the correctness of proposed analytical formulation.

  12. 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.

  13. Performance of a space-time block coded code division multiple access system over Nakagami-m fading channels

    NASA Astrophysics Data System (ADS)

    Yu, Xiangbin; Dong, Tao; Xu, Dazhuan; Bi, Guangguo

    2010-09-01

    By introducing an orthogonal space-time coding scheme, multiuser code division multiple access (CDMA) systems with different space time codes are given, and corresponding system performance is investigated over a Nakagami-m fading channel. A low-complexity multiuser receiver scheme is developed for space-time block coded CDMA (STBC-CDMA) systems. The scheme can make full use of the complex orthogonality of space-time block coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, the average bit error rate (BER) of the system is derived in detail for integer m and non-integer m, respectively. As a result, a tight closed-form BER expression is obtained for STBC-CDMA with an orthogonal spreading code, and an approximate closed-form BER expression is attained for STBC-CDMA with a quasi-orthogonal spreading code. Simulation results show that the proposed scheme can achieve almost the same performance as the existing scheme with low complexity. Moreover, the simulation results for average BER are consistent with the theoretical analysis.

  14. A Reliability Study of RFID Technology in a Fading Channel

    DTIC Science & Technology

    2007-06-01

    systems. Bit and tag error probabilities are computed for various OOK and M-CSK modulation schemes in a varying Nakagami - m fading channel, and the best...performing schemes are identified for future employment. 15. NUMBER OF PAGES 69 14. SUBJECT TERMS RFID, Fading Channel, Nakagami , On-off...and tag error probabilities are computed for various OOK and M-CSK modulation schemes in a varying Nakagami - m fading channel, and the best performing

  15. Optimal Power Allocation for CC-HARQ-based Cognitive Radio with Statistical CSI in Nakagami Slow Fading Channels

    NASA Astrophysics Data System (ADS)

    Xu, Ding; Li, Qun

    2017-01-01

    This paper addresses the power allocation problem for cognitive radio (CR) based on hybrid-automatic-repeat-request (HARQ) with chase combining (CC) in Nakagamimslow fading channels. We assume that, instead of the perfect instantaneous channel state information (CSI), only the statistical CSI is available at the secondary user (SU) transmitter. The aim is to minimize the SU outage probability under the primary user (PU) interference outage constraint. Using the Lagrange multiplier method, an iterative and recursive algorithm is derived to obtain the optimal power allocation for each transmission round. Extensive numerical results are presented to illustrate the performance of the proposed algorithm.

  16. Reliability of a jammed binary transmission over a Nakagami channel

    NASA Astrophysics Data System (ADS)

    Zenon, Syroka

    2014-05-01

    This study presents a mathematic and numerical analysis of the probability of error in a binary transmission over a fading radio channel described by Nakagami-m distribution and its special cases. The transmission is jammed by a signal occupying the entire (or comparable) band before detection.

  17. Distortion outage minimization in Nakagami fading using limited feedback

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Hong; Dey, Subhrakanti

    2011-12-01

    We focus on a decentralized estimation problem via a clustered wireless sensor network measuring a random Gaussian source where the clusterheads amplify and forward their received signals (from the intra-cluster sensors) over orthogonal independent stationary Nakagami fading channels to a remote fusion center that reconstructs an estimate of the original source. The objective of this paper is to design clusterhead transmit power allocation policies to minimize the distortion outage probability at the fusion center, subject to an expected sum transmit power constraint. In the case when full channel state information (CSI) is available at the clusterhead transmitters, the optimization problem can be shown to be convex and is solved exactly. When only rate-limited channel feedback is available, we design a number of computationally efficient sub-optimal power allocation algorithms to solve the associated non-convex optimization problem. We also derive an approximation for the diversity order of the distortion outage probability in the limit when the average transmission power goes to infinity. Numerical results illustrate that the sub-optimal power allocation algorithms perform very well and can close the outage probability gap between the constant power allocation (no CSI) and full CSI-based optimal power allocation with only 3-4 bits of channel feedback.

  18. Performance Analysis of IEEE 802.11g Waveform Transmitted Over a Fading Channel with Pulse-Noise Interference

    DTIC Science & Technology

    2006-06-01

    transmitted over a slow, flat fading Nakagami channel for AWGN only, as well as for AWGN plus pulse-noise interference. The implementation of forward...noise power. 15. NUMBER OF PAGES 123 14. SUBJECT TERMS IEEE 802.11g WLAN Standard, Nakagami Fading Channel, OFDM, Soft Decision Decoding, Pulse...their performance with Viterbi soft decision decoding when the signal was transmitted over a slow, flat fading Nakagami channel for additive white

  19. Outage Probability of SINR for Underlay Cognitive Radio Systems in Nakagami Fading

    NASA Astrophysics Data System (ADS)

    Jarrouj, Jiana; Blagojevic, Vesna; Ivanis, Predrag

    2014-11-01

    In this paper underlay cognitive radio system is analyzed in Nakagami fading environment, for the case when the available channel state information (CSI) of the link from the secondary transmitter to the primary receiver is outdated. We considered the case when both interference and transmit power constraints are applied. The impact of the co-channel interference that originates from the primary user is analyzed in details. The exact closed-form expressions for probability density function, outage probability, and the moments of signal-to-interference and noise ratio (SINR) at the secondary user's receiver are derived. The analytical expressions are verified by using independent Monte Carlo simulation method.

  20. Performance Analysis of Beamforming in Fixed-gain AF Relay Networks with Asymmetric Correlated Fading Channels

    NASA Astrophysics Data System (ADS)

    Li, Min

    2014-07-01

    In this paper, the performance of beamforming (BF) for a dual-hop amplify-and-forward (AF) relay network, where the source and destination are each equipped with multiple antennas, is investigated. It is assumed that the source-relay and relay-destination channels experience mixed fading distributions, namely, correlated Nakagami-m/Rician and correlated Rician/Nakagami-m, respectively. By considering fixed-gain relaying, analytical expressions for outage probability (OP) and average symbol error rate (ASER) are derived in closed-form. Numerical results are presented to demonstrate the efficacy of our performance analysis, also illustrate the impact of channel correlation, fading severity, Rician factor and antenna configuration on the performance of the system. It is shown that the correlated Nakagami-m/Rician fading channel can achieve better performance than the correlated Rician/Nakagami-m fading channel with the increase of fading severity parameter, and the correlated Rician/Nakagami-m fading channel may outperform the correlated Nakagami-m/Rician fading channel by enlarging the Rician factor.

  1. An Alternative Method to Compute the Bit Error Probability of Modulation Schemes Subject to Nakagami-[InlineEquation not available: see fulltext.] Fading

    NASA Astrophysics Data System (ADS)

    Queiroz, Wamberto J. L.; Lopes, Waslon T. A.; Madeiro, Francisco; Alencar, Marcelo S.

    2010-12-01

    This paper presents an alternative method for determining exact expressions for the bit error probability (BEP) of modulation schemes subject to Nakagami-[InlineEquation not available: see fulltext.] fading. In this method, the Nakagami-[InlineEquation not available: see fulltext.] fading channel is seen as an additive noise channel whose noise is modeled as the ratio between Gaussian and Nakagami-[InlineEquation not available: see fulltext.] random variables. The method consists of using the cumulative density function of the resulting noise to obtain closed-form expressions for the BEP of modulation schemes subject to Nakagami-[InlineEquation not available: see fulltext.] fading. In particular, the proposed method is used to obtain closed-form expressions for the BEP of [InlineEquation not available: see fulltext.]-ary quadrature amplitude modulation ([InlineEquation not available: see fulltext.]-QAM), [InlineEquation not available: see fulltext.]-ary pulse amplitude modulation ([InlineEquation not available: see fulltext.]-PAM), and rectangular quadrature amplitude modulation ([InlineEquation not available: see fulltext.]-QAM) under Nakagami-[InlineEquation not available: see fulltext.] fading. The main contribution of this paper is to show that this alternative method can be used to reduce the computational complexity for detecting signals in the presence of fading.

  2. 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.

  3. Error Probability of MRC in Frequency Selective Nakagami Fading in the Presence of CCI and ACI

    NASA Astrophysics Data System (ADS)

    Rahman, Mohammad Azizur; Sum, Chin-Sean; Funada, Ryuhei; Sasaki, Shigenobu; Baykas, Tuncer; Wang, Junyi; Harada, Hiroshi; Kato, Shuzo

    An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.

  4. Outage Analysis of Dual-hop Cognitive Networks with Relay Selection over Nakagami-m Fading Environment

    NASA Astrophysics Data System (ADS)

    Zhang, Zongsheng; Pi, Xurong

    2014-09-01

    In this paper, we investigate the outage performance of decode-and-forward cognitive relay networks for Nakagami-m fading channels, with considering both best relay selection and interference constraints. Focusing on the relay selection and making use of the underlay cognitive approach, an exact closed-form outage probability expression is derived in an independent, non-identical distributed Nakagami-m environment. The closed-form outage probability provides an efficient means to evaluate the effects of the maximum allowable interference power, number of cognitive relays, and channel conditions between the primary user and cognitive users. Finally, we present numerical results to validate the theory analysis. Moreover, from the simulation results, we obtain that the system can obtain the full diversity.

  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. A Simple Exact Error Rate Analysis for DS-CDMA with Arbitrary Pulse Shape in Flat Nakagami Fading

    NASA Astrophysics Data System (ADS)

    Rahman, Mohammad Azizur; Sasaki, Shigenobu; Kikuchi, Hisakazu; Harada, Hiroshi; Kato, Shuzo

    A simple exact error rate analysis is presented for random binary direct sequence code division multiple access (DS-CDMA) considering a general pulse shape and flat Nakagami fading channel. First of all, a simple model is developed for the multiple access interference (MAI). Based on this, a simple exact expression of the characteristic function (CF) of MAI is developed in a straight forward manner. Finally, an exact expression of error rate is obtained following the CF method of error rate analysis. The exact error rate so obtained can be much easily evaluated as compared to the only reliable approximate error rate expression currently available, which is based on the Improved Gaussian Approximation (IGA).

  7. Performance Analysis of IEEE 802.11g TCM Waveforms Transmitted over a Channel with Pulse-Noise Interference

    DTIC Science & Technology

    2007-06-01

    SYSTEM WITH r=2/3 CONVOLUTION CODING AND 8-PSK MODULATION IN AWGN AND PNI FOR FLAT, SLOWLY FADING NAKAGAMI CHANNELS ..................... 23 A...26 3. Probability Bit Error with Hard Decision Decoding for Flat, Slowly Fading Nakagami Channels...and AWGN ........................... 33 4. Probability Bit Error with Hard Decision Decoding for Flat, Slowly Fading Nakagami Channels with both AWGN

  8. On Statistics of Log-Ratio of Arithmetic Mean to Geometric Mean for Nakagami-m Fading Power

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Cheng, Julian; Tellambura, Chintha

    To assess the performance of maximum-likelihood (ML) based Nakagami m parameter estimators, current methods rely on Monte Carlo simulation. In order to enable the analytical performance evaluation of ML-based m parameter estimators, we study the statistical properties of a parameter Δ, which is defined as the log-ratio of the arithmetic mean to the geometric mean for Nakagami-m fading power. Closed-form expressions are derived for the probability density function (PDF) of Δ. It is found that for large sample size, the PDF of Δ can be well approximated by a two-parameter Gamma PDF.

  9. OFDM Transmission Characteristics where the Delay Profile Exceeds the Guard Interval in Nakagami-Rice Fading Environment

    NASA Astrophysics Data System (ADS)

    Karasawa, Yoshio; Vanmany, Changarkame

    In order to evaluate the effect of Nakagami-Rice fading on Orthogonal Frequency Division Multiplex (OFDM) signal transmission when the delay profile exceeds the guard interval, a simple prediction model is developed by extending the Equivalent Transmission-Path (ETP) model for Rayleigh fading. The validity of the model is demonstrated by comparing the calculated values of BER to those obtained by computer simulation. Using the newly developed ETP-OFDM model, digital transmission characteristics of the OFDM signal in a multipath environment when the delay profile exceeds the guard interval are shown as a function of K factor, delay spread, guard interval and OFDM symbol period.

  10. Hardware Emulation of Wireless Communication Fading Channels

    DTIC Science & Technology

    2011-01-01

    vol. 19, no. 6 , pp. 1009-1018, Jun. 2001. [9] B. E. Baddour and N. C. Beaulieu, “Accurate simulation of multiple cross- correlated Rician fading...Rayleigh fading waveforms,” IEEE Trans. Commun., vol. 6 , no. 6 , pp. 256-258, Nov. 2002. [18] Y. R. Zheng and C. Xiao, “ Simulation models with correct...waveforms in the baseband equivalent channel due to the bandlimited nature of wireless systems [ 6 ]. Software-based channel simulators usually employ

  11. 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 .

  12. On the performance analysis of SSC diversity system over η-μ fading channels

    NASA Astrophysics Data System (ADS)

    Khatalin, Sari

    2016-06-01

    In this paper, we study key performance measures of dual-branch switch-and-stay combining (SSC) system operating in ? fading environment. Specifically, analytical expressions for the kth order moment, average signal-to-noise ratio, amount of fading and outage probability are obtained for an SSC system operating over ? fading channels. Expressions of the average bit error rate (BER) for coherent detection and non-coherent detection were also derived with SSC for various modulation schemes. The BER expressions for the coherent detection case were derived using the moment generating function-based approach. Some of the final expressions are presented in the form of infinite series. Therefore, those series are truncated and upper bounds are derived for truncation errors. Expressions to determine the optimum adaptive switching thresholds are also presented. Corresponding results for Nakagami-q and Nakagami-m fading are derived in this paper as special cases. Numerical results are provided to demonstrate the applications of the new results.

  13. Consensus Algorithms Over Fading Channels

    DTIC Science & Technology

    2010-10-01

    studying the effect of fading and collisions on the performance of wireless consensus gossiping and in comparing its cost (measured in terms of number of...not assumed to be symmetric under A2. III. RELATED WORK There has been a resurgence of interest in characterizing consen- sus and gossip algorithms...tree, and then distribute the consensus value, with a finite number of exchanges. The price paid is clearly that of finding the appropriate routing

  14. 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.

  15. 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.

  16. 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

  17. Performance of Digital Communications over Selective Fading Channels.

    DTIC Science & Technology

    1983-09-01

    J. G. Proakis , Digital Communications, McGraw-Hill, New York, 1983. ’ [45] R. D. Gitlin, E. Y. Ho and 3. E. Mazo, "Passband equalization of...7 D-A142 427 PERFORNANCE OF DIGITAL COMMUNICATIONS OVER SELECTIVE 1/2 FADING CHRNNELS(U) ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB F D GARBER...PERIOD COVERED Technical Report PERFORMANCE OF DIGITAL COMMUNICATIONS OVER 6. PERFORMING ORG. REPORT NUMBER SELECTIVE FADING CHANNELS R-998; UILU-ENG

  18. 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

  19. 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.

  20. 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.

  1. New 16-PSK trellis codes for fading channels

    NASA Technical Reports Server (NTRS)

    Du, Jun; Vucetic, Branka; Zhang, Lin

    1990-01-01

    Growth in satellite mobile communications leads to increasing requirements for high data rate transmission that can be met by more efficient modulation schemes (M greater than 8). The 16-PSK trellis coded modulation technique is a very promising solution. A class of new 16-PSK trellis codes with improved error rate are designed based on the criteria on fading channels.

  2. Blind Equalization and Fading Channel Signal Recovery of OFDM Modulation

    DTIC Science & Technology

    2011-03-01

    subchannel is affected by flat-fading, which can be easily equalized. A guard time interval between symbols prevents inter-symbol interference...provided in this chapter. The principle behind OFDM is the idea that a wideband frequency channel can be divided into subchannels with narrower...investigated a DFT-based adaptive method for channel estimation. The next chapter discusses an algorithm for the estimation of data in null subchannels

  3. Convolutional fountain distribution over fading wireless channels

    NASA Astrophysics Data System (ADS)

    Usman, Mohammed

    2012-08-01

    Mobile broadband has opened the possibility of a rich variety of services to end users. Broadcast/multicast of multimedia data is one such service which can be used to deliver multimedia to multiple users economically. However, the radio channel poses serious challenges due to its time-varying properties, resulting in each user experiencing different channel characteristics, independent of other users. Conventional methods of achieving reliability in communication, such as automatic repeat request and forward error correction do not scale well in a broadcast/multicast scenario over radio channels. Fountain codes, being rateless and information additive, overcome these problems. Although the design of fountain codes makes it possible to generate an infinite sequence of encoded symbols, the erroneous nature of radio channels mandates the need for protecting the fountain-encoded symbols, so that the transmission is feasible. In this article, the performance of fountain codes in combination with convolutional codes, when used over radio channels, is presented. An investigation of various parameters, such as goodput, delay and buffer size requirements, pertaining to the performance of fountain codes in a multimedia broadcast/multicast environment is presented. Finally, a strategy for the use of 'convolutional fountain' over radio channels is also presented.

  4. Utilizing space frequency COFDM on multipath fading channels

    NASA Astrophysics Data System (ADS)

    Kellerman, Fred C.

    2007-04-01

    This paper will investigate the use of an enhanced rate one Alamouti Space Frequency (SF) multiple antenna Orthogonal Frequency Division Multiplex (OFDM) radio communication system. A two transmit, single receive antenna system will be simulated to operate under conditions of multipath fading with noise. A simple modification to the standard coherent Alamouti receive combiner will be applied and shown to improve bit error rate (BER) performance on rapidly fading multipath HF channels. Orthogonal Frequency Division Multiplexing frequency domain techniques will be utilized to effectively eliminate the Inter-Symbol Interference (ISI) resulting from the effects of multipath. Numerically simulated results will be shown for several multipath fading High Frequency (HF) radio channels. Inner convolutional error correction coding will be applied in addition to the Alamouti coding and numerically simulated BER results presented. Various HF channel conditions will be simulated including the 2 ms, 10 Hz, 2 ms, 5 Hz, CCIR poor (2 ms, 1 Hz) and extra poor (2 ms, 2 Hz) channel conditions. Performance under conditions of correlated transmit antennas will also be investigated.

  5. 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

  6. 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.

  7. Outage Probability of MRC for κ-μ Shadowed Fading Channels under Co-Channel Interference

    PubMed Central

    Chen, Changfang; Shu, Minglei; Wang, Yinglong; Yang, Ming; Zhang, Chongqing

    2016-01-01

    In this paper, exact closed-form expressions are derived for the outage probability (OP) of the maximal ratio combining (MRC) scheme in the κ-μ shadowed fading channels, in which both the independent and correlated shadowing components are considered. The scenario assumes the received desired signals are corrupted by the independent Rayleigh-faded co-channel interference (CCI) and background white Gaussian noise. To this end, first, the probability density function (PDF) of the κ-μ shadowed fading distribution is obtained in the form of a power series. Then the incomplete generalized moment-generating function (IG-MGF) of the received signal-to-interference-plus-noise ratio (SINR) is derived in the closed form. By using the IG-MGF results, closed-form expressions for the OP of MRC scheme are obtained over the κ-μ shadowed fading channels. Simulation results are included to validate the correctness of the analytical derivations. These new statistical results can be applied to the modeling and analysis of several wireless communication systems, such as body centric communications. PMID:27851817

  8. 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.

  9. 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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Fading losses on the LCRD free-space optical link due to channel turbulence

    NASA Astrophysics Data System (ADS)

    Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon

    2013-03-01

    The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Optical turbulence over the communication paths will cause random uctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by optical turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.

  15. Fading Losses on the LCRD Free-Space Optical Link Due to Channel Turbulence

    NASA Technical Reports Server (NTRS)

    Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon

    2013-01-01

    The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Clear air turbulence over the communication paths will cause random fluctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by clear air turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.

  16. Performance of FH/BFSK with generalized fading in worst case partial-band Gaussian interference

    NASA Astrophysics Data System (ADS)

    Crepeau, Paul J.

    1990-06-01

    For frequency-hopped (noncoherent) binary frequency shift keying (FH/BFSK) on a worst-case partial-band Gaussian interference channel, the bit error probability results are well known for the extreme cases where the signal is either nonfading or Rayleigh fading. In this work, the region between these extremes is filled in by considering the general Nakagami-m fading model. The worst-case partial-band Gaussian interference results are given by a one-parameter family which for m goes to infinity gives the Viterbi-Jacobs nonfading result, and for m = 1 gives the Rayleigh fading result. In the latter case, a broadband interference strategy is optimal. Thus, the Nakagami-m results provide a smooth one-parameter bridge between the Viterbi-Jacobs channel and the Rayleigh fading channel. The results show that the worst-case interference fraction rho increases as the fading variance increases, up to Rayleigh fading. Any fading less severe than Rayleigh, however slight the departure from Rayleigh, requires a partial-band strategy for sufficiently large Eb/NI.

  17. 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.

  18. Communications by vocoder on a mobile satellite fading channel

    NASA Astrophysics Data System (ADS)

    dal Degan, N.; Perosino, F.; Rusina, F.

    The performance of a LPC vocoder system is analyzed under various bit rate and fading errors. The error generation model developed to estimate error probability, and length of error bursts and distributions is described. Two algorithms that will improve burst are proposed. The evaluation of the spectral distance measures of the voice coding system is examined. The intelligibility, quality, and acceptability of the system are assessed using the mean opinion scores method.

  19. Performance of convolutional codes on fading channels typical of planetary entry missions

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    The performance of convolutional codes in fading channels typical of the planetary entry channel is examined in detail. The signal fading is due primarily to turbulent atmospheric scattering of the RF signal transmitted from an entry probe through a planetary atmosphere. Short constraint length convolutional codes are considered in conjunction with binary phase-shift keyed modulation and Viterbi maximum likelihood decoding, and for longer constraint length codes sequential decoding utilizing both the Fano and Zigangirov-Jelinek (ZJ) algorithms are considered. Careful consideration is given to the modeling of the channel in terms of a few meaningful parameters which can be correlated closely with theoretical propagation studies. For short constraint length codes the bit error probability performance was investigated as a function of E sub b/N sub o parameterized by the fading channel parameters. For longer constraint length codes the effect was examined of the fading channel parameters on the computational requirements of both the Fano and ZJ algorithms. The effects of simple block interleaving in combatting the memory of the channel is explored, using the analytic approach or digital computer simulation.

  20. 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.

  1. 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.

  2. A free-space optical terminal for fading channels

    NASA Astrophysics Data System (ADS)

    Williams, T.; Murphy, R. J.; Walther, F.; Volpicelli, A.; Wilcox, B.; Crucioli, D.

    2009-08-01

    This paper describes a lasercom terminal using spatial diversity to mitigate fading caused by atmospheric scintillation. Multiple receive apertures are separated sufficiently to capture statistically independent samples of the incoming beam. The received optical signals are tracked individually, photo-detected, and summed electrically, with measured diversity gain. The terminal consists of COTS components. It was used in successful demonstrations over a 5.4km ground-ground link from June through September 2008, during which it experienced a wide temperature range. Design overview and hardware realization are presented. This work was sponsored by the Department of Defense, RRCO DDR&E, under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the United States Government.

  3. Approximate Minimum Bit Error Rate Equalization for Fading Channels

    NASA Astrophysics Data System (ADS)

    Kovacs, Lorant; Levendovszky, Janos; Olah, Andras; Treplan, Gergely

    2010-12-01

    A novel channel equalizer algorithm is introduced for wireless communication systems to combat channel distortions resulting from multipath propagation. The novel algorithm is based on minimizing the bit error rate (BER) using a fast approximation of its gradient with respect to the equalizer coefficients. This approximation is obtained by estimating the exponential summation in the gradient with only some carefully chosen dominant terms. The paper derives an algorithm to calculate these dominant terms in real-time. Summing only these dominant terms provides a highly accurate approximation of the true gradient. Combined with a fast adaptive channel state estimator, the new equalization algorithm yields better performance than the traditional zero forcing (ZF) or minimum mean square error (MMSE) equalizers. The performance of the new method is tested by simulations performed on standard wireless channels. From the performance analysis one can infer that the new equalizer is capable of efficient channel equalization and maintaining a relatively low bit error probability in the case of channels corrupted by frequency selectivity. Hence, the new algorithm can contribute to ensuring QoS communication over highly distorted channels.

  4. Fading probability density function of free-space optical communication channels with pointing error

    NASA Astrophysics Data System (ADS)

    Zhao, Zhijun; Liao, Rui

    2011-06-01

    The turbulent atmosphere causes wavefront distortion, beam wander, and beam broadening of a laser beam. These effects result in average power loss and instantaneous power fading at the receiver aperture and thus degrade performance of a free-space optical (FSO) communication system. In addition to the atmospheric turbulence, a FSO communication system may also suffer from laser beam pointing error. The pointing error causes excessive power loss and power fading. This paper proposes and studies an analytical method for calculating the FSO channel fading probability density function (pdf) induced by both atmospheric turbulence and pointing error. This method is based on the fast-tracked laser beam fading profile and the joint effects of beam wander and pointing error. In order to evaluate the proposed analytical method, large-scale numerical wave-optics simulations are conducted. Three types of pointing errors are studied , namely, the Gaussian random pointing error, the residual tracking error, and the sinusoidal sway pointing error. The FSO system employs a collimated Gaussian laser beam propagating along a horizontal path. The propagation distances range from 0.25 miles to 2.5 miles. The refractive index structure parameter is chosen to be Cn2 = 5×10-15m-2/3 and Cn2 = 5×10-13m-2/3. The studied cases cover from weak to strong fluctuations. The fading pdf curves of channels with pointing error calculated using the analytical method match accurately the corresponding pdf curves obtained directly from large-scale wave-optics simulations. They also give accurate average bit-error-rate (BER) curves and outage probabilities. Both the lognormal and the best-fit gamma-gamma fading pdf curves deviate from those of corresponding simulation curves, and they produce overoptimistic average BER curves and outage probabilities.

  5. 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.

  6. Multiple trellis coded modulation (MTCM) performance on a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K.; Divsalar, Dariush

    1987-01-01

    The author recently introduced the notion of multiple trellis coding, in which more than one channel symbol per trellis branch is transmitted. He showed that on the ideal additive white Gaussian noise (AWGN) channel, the combination of multiple trellis coding with M-ary modulation yields a performance gain with symmetric signal sets comparable to and in some cases better than that previously achieved only with signal constellation asymmetry. The combination of conventional trellis coding with multiple phase-shift-keyed (MPSK) signaling has recently been shown by the author to be a well-suited modulation/coding scheme for transmission over the fading mobile satellite channel. In particular, a rate 2/3 coded 8-PSK scheme operating at 4800 b/s is currently under development for use in NASA's Mobile Satellite Experiment (MSAT-X). The author applies the multiple trellis-coded modulation technique in the same fading mobile satellite environment, extending the analysis results previously found for its performance over the AWGN channel to the MSAT-X channel.

  7. 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.

  8. On the First and the Second Order Statistics of the Capacity of κ-μ Fading Channels

    NASA Astrophysics Data System (ADS)

    Panić, Stefan; Stefanović, Mihajlo; Vasić, Selena; Milić, Dejan; Cvetković, Aleksandar

    2014-09-01

    Consideration of the channel capacity temporal behavior, in order to design a system that could adapt the transmission rate according to the capacity evolving process, and could transmit close to the ergodic capacity, is provided in this paper. Channel conditions have been modeled by the recently introduced general κ-μ fading model. We have studied statistical properties of the capacity of κ-μ fading channels. Analytical expressions for the first order statistical properties: probability density function (PDF), cumulative distribution function (CDF) and the outage capacity (OC), as well as the second-order statistical properties, such as the level-crossing rate (LCR), and average fade duration (AFD) of the instantaneous channel capacity, have been derived. Obtained results are numerically presented and visualized by the corresponding graphs.

  9. Efficiency of MIMO configuration and adaptive optics corrections in free space optical fading channels

    NASA Astrophysics Data System (ADS)

    Hajjarian, Zeinab; Kavehrad, Mohsen; Fadlullah, Jarir

    2010-01-01

    Free Space Optical (FSO) communications is the only practical candidate for realizing universal network coverage between ground and airborne nodes, satellites, and even moon and other nearby planets. When atmosphere (be it the earth or Mars) is a part of the optical channel, attributes of scattering and turbulence bring about amplitude attenuation, and scintillation, as well as beam wander and phase aberrations at the receiving aperture. Phase screens are usually used in order to simulate the atmospheric fading channel and phase fluctuations. In this paper, different methods of generating phase screens are compared based on their accuracy and computational complexity, as in most computer simulations, a large ensemble of phase screens are required for averaging purposes. To combat the focal plane intensity fading, caused by amplitude and phase variations in the received wave-front, it is possible to replace the Single Input-Single Output (SISO) communications system with its Multiple Input Multiple Output (MIMO) equivalent, which has the same total transmit power and receiving aperture area. Another alternative is to equip the receiver with a state of the art Adaptive Optics (AO) correction system. Using average Bit Error Rate (BER), as a performance metric, effectiveness of these two approaches are compared and it is shown that while a MIMO configuration outperforms a basic AO system capable of only tilt corrections, an ideal AO system, which is able to remove higher orders of Zernike modes can asymptotically perform as well as an equivalent MIMO configuration.

  10. On fading probability density functions of fast-tracked and untracked free-space optical communication channels

    NASA Astrophysics Data System (ADS)

    Zhao, Zhijun; Liao, Rui

    2011-03-01

    Free-space optical (FSO) communication systems suffer from average power loss and instantaneous power fading due to the atmospheric turbulence. The channel fading probability density function (pdf) is of critical importance for FSO communication system design and evaluation. The performance and reliability of FSO communication systems can be greatly enhanced if fast-tacking devices are employed at the transmitter in order to compensate laser beam wander at the receiver aperture. The fast-tracking method is especially effective when communication distance is long. This paper studies the fading probability density functions of both fast-tracked and untracked FSO communication channels. Large-scale wave-optics simulations are conducted for both tracked and untracked lasers. In the simulations, the Kolmogorov spectrum is adopted, and it is assumed that the outer scale is infinitely large and the inner scale is negligibly small. The fading pdfs of both fast-tracked and untracked FSO channels are obtained from the simulations. Results show that the fast-tracked channel fading can be accurately modeled as gamma-distributed if receiver aperture size is smaller than the coherence radius. An analytical method is given for calculating the untracked fading pdfs of both point-like and finite-size receiver apertures from the fast-tracked fading pdf. For point-like apertures, the analytical method gives pdfs close to the well-known gamma-gamma pdfs if off-axis effects are omitted in the formulation. When off-axis effects are taken into consideration, the untracked pdfs obtained using the analytical method fit the simulation pdfs better than gamma-gamma distributions for point-like apertures, and closely fit the simulation pdfs for finite-size apertures where gamma-gamma pdfs deviate from those of the simulations significantly.

  11. Trellis coded modulation for 4800-9600 bits/s transmission over a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Simon, Marvin K.

    1987-01-01

    The combination of trellis coding and multiple phase-shift-keyed (MPSK) signaling 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.

  12. Frequency Tracking Performance Using a Hyperbolic Digital-Phase Locked Loop for Ka-Band Communication in Rain Fading Channels

    NASA Astrophysics Data System (ADS)

    Sithamparanathan, Kandeepan; Piesiewicz, Radoslaw

    In this paper we study and present some results on the performances of frequency tracking for Ka-band satellite communications in rain fading channels. The carrier frequency is tracked using a 2nd order hyperbolic phase detector based digital-phase locked loop (D-PLL). The hyperbolic D-PLL has the capability of extending the tracking range compared to the other D-PLL and hence can be designed such that to achieve low phase jitter performance for improved carrier tracking. We present the design and analysis of the D-PLL and show some simulation results on the frequency tracking performance for Ka-band rain fading channel. The results are compared with the non-fading noise only case and comparative analyses are made.

  13. 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.

  14. 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.

  15. Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links

    NASA Astrophysics Data System (ADS)

    Toyoshima, Morio; Takenaka, Hideki; Takayama, Yoshihisa

    2011-08-01

    The fading channel model for generating a random time-varying signal based on the atmospheric turbulence spectrum for space-to-ground laser links is discussed. The temporal frequency characteristics of the downlink are theoretically derived based on the von Karman spectrum. The rms wind speed based on the Bufton wind model is used as the transverse wind velocity, which makes the simulation simple. The time-varying signal is generated as functions of the receiver aperture diameter and the rms wind speed. The simulated result of the time-varying signal is presented and compared with the gamma-gamma distribution based on the scintillation theory in a moderate-to-strong-turbulence regime.

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

    NASA Technical Reports Server (NTRS)

    Park, Sangil; Messer, Dion D.

    1990-01-01

    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.

  17. 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

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

    PubMed

    Ren, Peng; Qian, Jiansheng

    2016-06-07

    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.

  19. Finite-Time Distributed State Estimation Over Sensor Networks With Round-Robin Protocol and Fading Channels.

    PubMed

    Xu, Yong; Lu, Renquan; Shi, Peng; Li, Hongyi; Xie, Shengli

    2016-12-15

    This paper considers finite-time distributed state estimation for discrete-time nonlinear systems over sensor networks. The Round-Robin protocol is introduced to overcome the channel capacity constraint among sensor nodes, and the multiplicative noise is employed to model the channel fading. In order to improve the performance of the estimator under the situation, where the transmission resources are limited, fading channels with different stochastic properties are used in each round by allocating the resources. Sufficient conditions of the average stochastic finite-time boundedness and the average stochastic finite-time stability for the estimation error system are derived on the basis of the periodic system analysis method and Lyapunov approach, respectively. According to the linear matrix inequality approach, the estimator gains are designed. Finally, the effectiveness of the developed results are illustrated by a numerical example.

  20. Improving the performance of continuous variable quantum key distribution using fading effects of free-space channel

    NASA Astrophysics Data System (ADS)

    Zhang, Zeyu; Zhu, Chengrui; He, Guangqiang

    2015-08-01

    Quantum key distribution can be used to share secret keys with information-theoretic security between two legitimate partners for secure communication. In the case of satellite communication, free-space channel is the only way to transmit information, thus research on its properties is of great significance to quantum cryptographic communication. In this paper, we thoroughly analyze the influence of free-space channel fading effects on continuous variable quantum key distribution and for the first time prove that random distribution (such as Rayleigh distribution, Rice distribution and et al.) of free-space channel fading coefficients can be used to increase secret information rates and improve system stability against excess noises. Our results offer academic reference for practical applications of ground-space and space-space quantum communication and global quantum communication network.

  1. Improved GOB synchronization for robust transmission of H.263 video over slow-fading channels

    NASA Astrophysics Data System (ADS)

    Abrardo, Andrea; Barni, Mauro; Garzelli, Andrea

    2001-10-01

    Among the techniques to limit the effect of error propagation in low bitrate video coding, the best performance is achieved through the joint use of forward error correction (FEC) and automatic repeat request strategies. However, retransmission of corrupted data introduces additional delay which may be critical in some practical applications. In such cases, only a FEC strategy is feasible at the expense of a significant increase of the overall transmission bit rate. In this paper, a strategy is proposed which instead of protecting the whole H.263 video stream, uses all the redundancy to protect the most important parts of the bit stream, i.e., group-of-block (GOB) start codes. More specifically, the 22-bit long start code used in the H.263 standard is replaced with longer Gold sequences which ensure a higher protection against noise. A different sequence is used for each GOB so that additional information can be obtained which can be used to improve the quality of the decoded sequence. The new technique is derived by assuming a slow-fading channel such as those encountered in pedestrian applications. Simulation results prove the effectiveness of the proposed technique with respect to classical FEC schemes in terms of PSNR and overall bit rate.

  2. 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.

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

    PubMed

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

    2011-07-04

    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.

  4. Comparative analysis of H.263 resilience techniques for H.223-based video transmission over slow-fading channels

    NASA Astrophysics Data System (ADS)

    Garzelli, Andrea; Abrardo, Andrea; Barni, Mauro; Marotta, D.

    2000-11-01

    The objective of this work is to analyze and compare H.263 resilience techniques for H.223-based real-time video transmission over narrow-band slow-fading channels. These channel conditions, which are typical for pedestrian video communications, are very critical, because they require Forward Error Correction (FEC), since data retransmission is not feasible, due to high network delay, and they reduce the effectiveness of FEC techniques- due to the bursty nature of the channel. In this work, two different strategies for H.263 video protection against channel errors are considered and compared. The strategies are tested over a slow-fading wireless channel, over which the H.263 video streams, organized and multiplexed by the H.223 Multiplex Protocol, are transmitted. Both standard FEC techniques considered by the H.223 recommendation for equal error protection of the video stream, and unequal error protection (UEP) through GOB synchronization are tested. The experimental results of this comparative analysis prove the superiority of the UEP technique for H.223-based video transmission.

  5. 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.

  6. Wavelength-diversity transmission for fading mitigation in the atmospheric optical communication channel

    NASA Astrophysics Data System (ADS)

    Giggenbach, Dirk; Wilkerson, Brandon L.; Henniger, Hennes; Perlot, Nicolas

    2006-08-01

    Mitigation of index of refraction turbulence (IRT) effects is crucial in long-range atmospheric communication links. Diversity-transmission is one favorable way for fading compensation. One of several different diversity concepts is the exploitation of the wavelength-dependent index of refraction of the atmosphere, which leads to ideal stochastically independent fading at different wavelengths, depending on the scenario. This concept is here named wavelength-diversity (WLD). Theoretical analysis and numerical simulation for the strength of this effect are given and verified by experimental tests.

  7. 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.

  8. Effect of filtering on the synchronization and performance of chaos-based secure communication over Rayleigh fading channel

    NASA Astrophysics Data System (ADS)

    Al-Hussaibi, Walid

    2015-09-01

    Chaos synchronization is one of the main challenging issues involved in the development of wireless chaos-based secure communication (CBSC) due its crucial influence on the error performance and system reliability. This paper is concerned with the effect of filtering chaotic signals on the synchronization and error performance of CBSC schemes due to the finite bandwidth of realistic fading channel and/or signal detection necessities. The double scroll chaotic attractor is employed at the transmit and receive terminals as in a drive-response configuration with identical synchronization and a low pass filter model is utilized in this investigation. The upper bound of bit error probability considering Rayleigh fading channel and synchronization mean squared error is derived and evaluated for different values of filter parameter. Theoretical analysis and simulation results show that as the filter cut-off frequency decreased lower than the chaotic signal bandwidth, the synchronization error is considerably increased due to high distortion in the normal geometrical configuration of the attractor. As a result, the average bit-error-rate performance is degraded significantly with high possibility of link failure. Therefore, careful system design should be made to mitigate the filtering effects and achieve the essential synchronization of promising CBSC systems.

  9. 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

  10. 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.

  11. Performance Analysis of a JTIDS/Link-16-type Waveform Transmitted over Slow, Flat Nakagami Fading Channels in the Presence of Narrowband Interference

    DTIC Science & Technology

    2008-12-01

    Probability of symbol error of the 32-chip CCSK sequence chosen for JTIDS in AWGN: Monte Carlo simulation versus analytical upper bound. ...66 Figure 22...Probability of symbol error for the 32-chip CCSK sequence chosen for JTIDS in AWGN: two different Monte Carlo simulations versus analytic upper...154 Figure 83. Probability of symbol error for CCSK (uncoded JTIDS ) with the new CCSK sequence in AWGN: analytic upper bound versus simulation

  12. Delay and throughput characteristics of TH, CDMA, TDMA, and hybrid networks for multipath faded data transmission channels

    NASA Astrophysics Data System (ADS)

    Elhakeem, Ahmed K.; Digirolamo, Rocco; Bdira, Ilyess B.; Talla, M.

    1994-05-01

    The new concepts of adaptive time hopping and variable frame Code Division (CDMA) Multiple Access are introduced. By a unified analysis, the probabilities of bit and packet errors in multipath fading environment for five Time Division (TDMA), Code Division, and Time Hopping (TH) related multiaccess networks are obtained; namely, TDMA, CDMA, CDMA/TDMA, Adaptive CDMA/TH, and variable frame CDMA/TDMA networks. The delay and useful throughputs of the five systems are also evaluated for data and voice traffic. All systems compared have the same channel power and bandwidth and support the same traffic. Though implementation issues are not covered, CDMA systems are put at a disadvantage (compared to cellular-type FDMA networks, for example) by ignoring such inherent advantages as voice silence utilizations and automatic frequency reuse. Nonetheless, two CDMA systems outperform TDMA systems at low and medium input traffics.

  13. On Frequency Offset Estimation Using the iNET Preamble in Frequency Selective Fading Channels

    DTIC Science & Technology

    2014-03-01

    ASM fields; (bottom) the relationship between the indexes of the received samples r(n), the signal samples s(n), the preamble samples p (n) and the short...frequency offset estimators for SOQPSK-TG equipped with the iNET preamble and operating in ISI channels. Four of the five estimators exam - ined here are...sync marker ( ASM ), and data bits (an LDPC codeword). The availability of a preamble introduces the possibility of data-aided synchro- nization in

  14. Unequal error protection codes for wavelet video transmission over W-CDMA, AWGN, and Rayleigh fading channels

    NASA Astrophysics Data System (ADS)

    Le, Minh Hung; Liyana-Pathirana, Ranjith

    2003-06-01

    The unequal error protection (UEP) codes with wavelet-based algorithm for video compression over wide-band code division multiple access (W-CDMA), additive white Gaussian noise (AWGN) and Rayleigh fading channels are analysed. The utilization of Wavelets has come out to be a powerful method for compress video sequence. The wavelet transform compression technique has shown to be more appropriate to high quality video applications, producing better quality output for the compressed frames of video. A spatially scalable video coding framework of MPEG2 in which motion correspondences between successive video frames are exploited in the wavelet transform domain. The basic motivation for our coder is that motion fields are typically smooth that can be efficiently captured through a multiresolutional framework. Wavelet decomposition is applied to video frames and the coefficients at each level are predicted from the coarser level through backward motion compensation. The proposed algorithms of the embedded zero-tree wavelet (EZW) coder and the 2-D wavelet packet transform (2-D WPT) are investigated.

  15. 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.

  16. 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

  17. Characterization of time delayed diversity to mitigate fading in atmospheric turbulence channels

    NASA Astrophysics Data System (ADS)

    Trisno, Sugianto; Smolyaninov, Igor I.; Milner, Stuart D.; Davis, Christopher C.

    2005-08-01

    Atmospheric turbulence is caused by inhomogeneities in the temperature and pressure of the atmosphere, resulting in random variations of the refractive index. A laser beam propagating through such turbulences experiences random amplitude and phase fluctuations, which can severely degrade the performance of free space optical (FSO) communication systems. In our time delayed diversity (TDD) technique, we transmit twice and take advantage of the fact that propagation along an atmospheric path is statistically uncorrelated with an earlier-time path for a time interval greater than the atmospheric turbulence correlation time. Communications performance is improved because the joint probability of error is less than the probability of error from individual channels. In this paper, we describe the theoretical and experimental analyses of FSO systems implementing this novel scheme in various performance scenarios. Theoretical models and performance of TDD systems are derived and characterized. The experimental performance results obtained under weak turbulence conditions are shown to be in good agreement with the theory. Related system design and implementation issues, such as: atmospheric turbulence statistics, laser beam depolarization, and diversity receiver architecture are also discussed.

  18. Simulation of Coherent Signals with Forward Error Correction Coding

    DTIC Science & Technology

    2007-03-01

    selective, slow Ricean fading channels in [4], frequency-selective, slow Nakagami fading channels in [5], and frequency-selective, slow Nakagami fading...selective, Slowly Fading Nakagami Channels,” Master’s Thesis, Naval Postgraduate School, Monterey, CA, 2001. 6 Kosa Irfan, “Performance of IEEE...802.11a Wireless LAN Standard over Frequency-selective, slowly fading Nakagami Channels in a pulsed jamming environment,” Master’s Thesis, Naval

  19. Fuzzy [Formula: see text] output-feedback control for the discrete-time system with channel fadings, sector nonlinearities, and randomly occurring interval delays and nonlinearities.

    PubMed

    Fan, Xiaozheng; Wang, Yan; Hu, Manfeng

    2016-01-01

    In this paper, the fuzzy [Formula: see text] output-feedback control problem is investigated for a class of discrete-time T-S fuzzy systems with channel fadings, sector nonlinearities, randomly occurring interval delays (ROIDs) and randomly occurring nonlinearities (RONs). A series of variables of the randomly occurring phenomena obeying the Bernoulli distribution is used to govern ROIDs and RONs. Meanwhile, the measurement outputs are subject to the sector nonlinearities (i.e. the sensor saturations) and we assume the system output is [Formula: see text], [Formula: see text]. The Lth-order Rice model is utilized to describe the phenomenon of channel fadings by setting different values of the channel coefficients. The aim of this work is to deal with the problem of designing a full-order dynamic fuzzy [Formula: see text] output-feedback controller such that the fuzzy closed-loop system is exponentially mean-square stable and the [Formula: see text] performance constraint is satisfied, by means of a combination of Lyapunov stability theory and stochastic analysis along with LMI methods. The proposed fuzzy controller parameters are derived by solving a convex optimization problem via the semidefinite programming technique. Finally, a numerical simulation is given to illustrate the feasibility and effectiveness of the proposed design technique.

  20. Probability of error analysis of digital partial response continuous phase modulation with two-bit differential detection and offset receiver diversity in fast Rayleigh fading channels

    NASA Astrophysics Data System (ADS)

    Elnoubi, Said M.

    1990-06-01

    The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems.

  1. Multi-pair two-way massive MIMO AF relaying with ZFR/ZFT beamforming and imperfect CSI over ricean fading channels

    NASA Astrophysics Data System (ADS)

    Xu, Kui; Sun, Xiaoli; Zhang, Dongmei

    2016-10-01

    This paper investigates the spectral and energy efficiencies of a multi-pair two-way amplify-and-forward (AF) relay system over Ricean fading channels, where multiple user-pairs exchange information within pair through a relay with very large number of antennas, while each user equipped with a single antenna. Firstly, beamforming matrixe of zero-forcing reception/zero-forcing transmission (ZFR/ZFT) with imperfect channel state information (CSI) at the relay is given. Then, the unified asymptotic signal-to-interference-plus-noise ratio (SINR) expressions with imperfect CSI are obtained analytically. Finally, two power scaling schemes are proposed and the asymptotic spectral and energy efficiencies based on the proposed power scaling schemes are derived and verified by the Monte-Carlo simulations. Theoretical analyses and simulation results show that with imperfect CSI, if the number of relay antennas grows asymptotically large, we need cut down the transmit power of each user and relay to different proportion when the Ricean K-factor is non-zero and zero (Rayleigh fading) in order to maintain a desirable rate.

  2. 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…

  3. 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…

  4. Statistical analysis on the optical fading in free space optical channel for RoFSO link design

    NASA Astrophysics Data System (ADS)

    Kim, Kyung-Hwan; Higashino, Takeshi; Tsukamoto, Katsutoshi; Komaki, Shozo; Kazaura, Kamugisha; Matsumoto, Mitsuji

    2010-01-01

    This paper presents empirical probability density functions (p.d.fs) of variance and fluctuation speed of scintillation, through analyzing a number of experimental data measured in Japan by a statistical model. The model enables us to treat scintillation speed by one parameter of cut-off frequency in the power spectral density (PDS). By using the model and based on the two p.d.fs, we also present simulation results on the level crossing rate (LCR) and average fade duration (AFD). Combined the two results, an outage probabilities corresponding to a threshold optical intensity can be derived.

  5. Performance of multi-hop parallel free-space optical communication over gamma-gamma fading channel with pointing errors.

    PubMed

    Gao, Zhengguang; Liu, Hongzhan; Ma, Xiaoping; Lu, Wei

    2016-11-10

    Multi-hop parallel relaying is considered in a free-space optical (FSO) communication system deploying binary phase-shift keying (BPSK) modulation under the combined effects of a gamma-gamma (GG) distribution and misalignment fading. Based on the best path selection criterion, the cumulative distribution function (CDF) of this cooperative random variable is derived. Then the performance of this optical mesh network is analyzed in detail. A Monte Carlo simulation is also conducted to demonstrate the effectiveness of the results for the average bit error rate (ABER) and outage probability. The numerical result proves that it needs a smaller average transmitted optical power to achieve the same ABER and outage probability when using the multi-hop parallel network in FSO links. Furthermore, the system use of more number of hops and cooperative paths can improve the quality of the communication.

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

    DOE PAGES

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

    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

  7. 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.

  8. Window-modulated compounding Nakagami imaging for ultrasound tissue characterization.

    PubMed

    Tsui, Po-Hsiang; Ma, Hsiang-Yang; Zhou, Zhuhuang; Ho, Ming-Chih; Lee, Yu-Hsin

    2014-08-01

    Ultrasound Nakagami parametric imaging is a useful tool for tissue characterization. Previous literature has suggested using a square with side lengths corresponding to 3 times the transducer pulse length as the minimum window for constructing the Nakagami image. This criterion does not produce sufficiently smooth images for the Nakagami image to characterize homogeneous tissues. To improve image smoothness, we proposed window-modulated compounding (WMC) Nakagami imaging based on summing and averaging the Nakagami images formed using sliding windows with varying window side lengths from 1 to N times the transducer pulse length in 1 pulse length step. Simulations (the number densities of scatterers: 2-16 scatterers/mm(2)) and experiments on fully developed speckle phantoms (the scatterer diameters: 20-106 μm) were conducted to suggest an appropriate number of frames N and to evaluate the image smoothness and resolution by analyzing the full width at half maximum (FWHM) of the parameter distribution and the widths of the image autocorrelation function (ACF), respectively. In vivo ultrasound measurements on rat livers without and with cirrhosis were performed to validate the practical performance of the WMC Nakagami image in tissue characterization. The simulation results showed that using a range of N from 7 to 10 as the number of frames for image compounding reduces the estimation error to less than 5%. Based on this criterion, the Nakagami parameter obtained from the WMC Nakagami image increased from 0.45 to 0.95 after increasing the number densities of scatterers from 2 to 16 scatterers/mm(2). The FWHM of the parameter distribution (bins=40) was 13.5±1.4 for the Nakagami image and 9.1±1.43 for the WMC Nakagami image, respectively (p-value<.05). The widths of the ACF for the Nakagami and WMC Nakagami images were 454±5.36 and 458±4.33, respectively (p-value>.05). In the phantom experiments, we also found that the FWHM of the parameter distribution for the WMC

  9. Three-dimensional ultrasonic Nakagami imaging for tissue characterization

    NASA Astrophysics Data System (ADS)

    Tsui, Po-Hsiang; Hsu, Cheng-Wei; Ho, Ming-Chih; Chen, Yung-Sheng; Lin, Jen-Jen; Chang, Chien-Cheng; Chu, Chin-Chou

    2010-10-01

    The two-dimensional (2D) Nakagami image complements the ultrasound B-scan image when attempting to visualize the scatterer properties of tissues. The resolution of the Nakagami image is lower than that of the B-scan image, since the former is produced by processing the raw envelope data using a 2D sliding window with side lengths typically corresponding to three times the pulse length of the incident ultrasound. This paper proposes using three-dimensional (3D) Nakagami imaging for improving the resolution of the obtained Nakagami image and providing more complete information of scatterers for a better tissue characterization. The 3D Nakagami image is based on a voxel array composed of the Nakagami parameters constructed using a 3D sliding cube to process the 3D backscattered raw data. Experiments on phantoms with different scatterer concentrations were carried out to determine the optimal size of the sliding cube for a stable estimation of the Nakagami parameter. Tissue measurements on rat livers without and with fibrosis formation were further used to explore the practical feasibility of 3D Nakagami imaging. The results indicated that the side length of the cube used to construct the 3D Nakagami image must be at least two times the pulse length, which improved the resolution for each Nakagami image frame in the 3D Nakagami image. The results further demonstrated that the 3D Nakagami image is better than the conventional 2D Nakagami image for complementing the B-scan in detecting spatial variations in the scatterer concentration and classifying normal and fibrotic livers. This study suggests that 3D Nakagami imaging has the potential to become a new 3D quantitative imaging approach.

  10. Three-dimensional ultrasonic Nakagami imaging for tissue characterization.

    PubMed

    Tsui, Po-Hsiang; Hsu, Cheng-Wei; Ho, Ming-Chih; Chen, Yung-Sheng; Lin, Jen-Jen; Chang, Chien-Cheng; Chu, Chin-Chou

    2010-10-07

    The two-dimensional (2D) Nakagami image complements the ultrasound B-scan image when attempting to visualize the scatterer properties of tissues. The resolution of the Nakagami image is lower than that of the B-scan image, since the former is produced by processing the raw envelope data using a 2D sliding window with side lengths typically corresponding to three times the pulse length of the incident ultrasound. This paper proposes using three-dimensional (3D) Nakagami imaging for improving the resolution of the obtained Nakagami image and providing more complete information of scatterers for a better tissue characterization. The 3D Nakagami image is based on a voxel array composed of the Nakagami parameters constructed using a 3D sliding cube to process the 3D backscattered raw data. Experiments on phantoms with different scatterer concentrations were carried out to determine the optimal size of the sliding cube for a stable estimation of the Nakagami parameter. Tissue measurements on rat livers without and with fibrosis formation were further used to explore the practical feasibility of 3D Nakagami imaging. The results indicated that the side length of the cube used to construct the 3D Nakagami image must be at least two times the pulse length, which improved the resolution for each Nakagami image frame in the 3D Nakagami image. The results further demonstrated that the 3D Nakagami image is better than the conventional 2D Nakagami image for complementing the B-scan in detecting spatial variations in the scatterer concentration and classifying normal and fibrotic livers. This study suggests that 3D Nakagami imaging has the potential to become a new 3D quantitative imaging approach.

  11. 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.

  12. 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

  13. 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.

  14. Beamforming effects on generalized Nakagami imaging.

    PubMed

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

    2015-10-07

    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

  15. Beamforming effects on generalized Nakagami imaging

    NASA Astrophysics Data System (ADS)

    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 for

  16. Digital Communications Over Fading Channels

    DTIC Science & Technology

    2007-11-02

    46 22 Exact and approximate performance of BPSK with continuous narrowband...1) M−1∑ n=1 (−1)n+1 n + 1 ( M − 1 n ) exp (−nγs n+ 1 ) ( 46 ) Substituting (14) and ( 46 ) into (10), we obtain Pb = M 2(M − 1) ∫ ∞ 0 M−1∑ n=1 (−1)n+1 n...average transmitted power is the same whether coded or uncoded bits are transmitted: EbcRbc = EbRb (60) Hence, Ebc = rEb (61) Since r < 1, the average

  17. Performance analysis of generalized QAM modulation under η-μ and κ-μ fading

    NASA Astrophysics Data System (ADS)

    L Queiroz, Wamberto J.; Madeiro, Francisco; A Lopes, Waslon T.; Alencar, Marcelo S.

    2013-12-01

    This paper presents new closed-form expressions for the symbol error probability (SEP) of θ-QAM modulation with maximum ratio combining (MRC) receiver under η- μ and κ- μ fading. The SEP formulae, obtained from the definite integrals of the moment generating function (MGF) of the signal-to-noise ratio (SNR) at the input of the MRC receiver, are written in terms of Lauricella functions. The numerical evaluation of the expressions is carried out for the η- μ distribution, which includes important distributions as special cases, such as Hoyt, Nakagami- m, Rayleigh, and one-sided Gaussian, as well as for the κ- μ distribution, which includes Rice, Nakagami- m, Rayleigh, and one-sided Gaussian as special cases.

  18. Measurement of satellite PCS fading using GPS

    NASA Astrophysics Data System (ADS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1995-08-01

    A six-channel commercial GPS receiver with a custom-made 40 deg tilted, rotating antenna has been assembled to make fade measurements for personal satellite communications. The system can measure up to two times per minute fades of up to 15 dB in the direction of each tracked satellite from 10 to 90 deg elevation. Photographic fisheye lens images were used to categorize the fade data obtained in several test locations according to fade states of clear, shadowed, or blocked. Multipath effects in the form of annular rings can be observed when most of the sky is clear. Tree fading by a Pecan exceeding 3.5 dB and 12 dB at 50 to 10 percent probability, respectively, compared with median fades of 7.5 dB measured earlier and the discrepancy is attributed to the change in ratio when measuring over an area as opposed to along a line. Data acquired inside buildings revealed 'rf-leaky' ceilings. Satellite diversity gain in a shadowed environment exceeded 6 dB at the 10 percent probability.

  19. Measurement of satellite PCS fading using GPS

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1995-01-01

    A six-channel commercial GPS receiver with a custom-made 40 deg tilted, rotating antenna has been assembled to make fade measurements for personal satellite communications. The system can measure up to two times per minute fades of up to 15 dB in the direction of each tracked satellite from 10 to 90 deg elevation. Photographic fisheye lens images were used to categorize the fade data obtained in several test locations according to fade states of clear, shadowed, or blocked. Multipath effects in the form of annular rings can be observed when most of the sky is clear. Tree fading by a Pecan exceeding 3.5 dB and 12 dB at 50 to 10 percent probability, respectively, compared with median fades of 7.5 dB measured earlier and the discrepancy is attributed to the change in ratio when measuring over an area as opposed to along a line. Data acquired inside buildings revealed 'rf-leaky' ceilings. Satellite diversity gain in a shadowed environment exceeded 6 dB at the 10 percent probability.

  20. Performance evaluation of ultrasonic Nakagami image in tissue characterization.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng; Chen, Wen-Shiang

    2008-04-01

    Conventional ultrasonic B-mode images qualitatively describe tissue structures but are unsuitable for quantitative analyses of scatterer properties. We have recently developed an ultrasonic parametric imaging technique based on the Nakagami statistical distribution that is able to quantify scatterer concentrations. The aim of the present study is to further explore both the behavior of a Nakagami image in characterizing different scatterer structures at different signal-to-noise ratios (SNRs) and the feasibility of Nakagami imaging using a general commercial ultrasound scanner for tissue examinations. Simulations, experiments on a tissue-mimicking phantom and in vitro measurements on a muscle tissue before and after microwave treatment were carried out. The SNR and contrast-to-noise ratio (CNR) were estimated to quantify image performance. The results demonstrate that a Nakagami image can differentiate different scatterer concentrations for single, hypoechoic and hyperechoic targets. Also, a Nakagami image, when combined with an ultrasound scanner, can complement the B-scan to characterize tissue and to identify the region of interest with a larger CNR. However, the noise effect can degrade the performance of a Nakagami image. When the signal SNR decreased to 15 dB in simulations and to 8 dB in experiments, the CNR of the hyperechoic Nakagami image decreased by 4% and 27%, respectively, and that of the hypoechoic one decreased by 42% and 80%, respectively. These results indicate that a Nakagami image behaves well in identifying regions with high scatterer concentrations but does not perform well when both the scatterer concentration and SNR are low.

  1. Imaging local scatterer concentrations by the Nakagami statistical model.

    PubMed

    Tsui, Po-Hsiang; Chang, Chien-Cheng

    2007-04-01

    The ultrasonic B-mode image is an important clinical tool used to examine the internal structures of the biological tissue. Due to the fact that the conventional B-scans cannot fully reflect the nature of the tissue, some useful quantitative parameters have been applied to quantify the properties of the tissue. Among various possibilities, the Nakagami parameter was demonstrated to have an outstanding ability to detect the variation of the scatterer concentration. This study is aimed to develop a scatterer concentration image based on the Nakagami parameter map to assist in the B-mode image for tissue characterization. In particular, computer simulations are carried out to generate phantoms of different scatterer concentrations and echogenicity coefficients and their B-mode and Nakagami parametric images are compared to evaluate the performance of the Nakagami image in differentiating the properties of the scatterers. The simulated results show that the B-mode image would be affected by the system settings and user operations, whereas the Nakagami parametric image provides a comparatively consistent image result when different diagnosticians use different dynamic ranges and system gains. This is largely because the Nakagami image formation is only based on the backscattered statistics of the ultrasonic signals in local tissues. Such an imaging principle allows the Nakagami image to quantify the local scatterer concentrations in the tissue and to extract the backscattering information from the regions of the weaker echoes that may be lost in the B-mode image. These findings suggest that the Nakagami image can be combined with the use of the B-mode image simultaneously to visualize the tissue structures and the scatterer properties for a better medical diagnosis.

  2. Completion Time Minimization and Robust Power Control in Wireless Packet Networks

    DTIC Science & Technology

    2008-12-18

    independent Rayleigh, Nakagami , or log-normal fading. I. INTRODUCTION Power control plays a crucial role in the operation of a wireless network, as it...concave in exponentiated channel power gains; e.g., when each user is under independent Rayleigh, Nakagami , or log-normal fading. 15. SUBJECT TERMS...probability constraint. We show that for a wide class of commonly used channel fading distributions, e.g., Rayleigh, Nakagami , and log-normal, robust

  3. Performance Analysis of IEEE 802.11g Receivers With Erasure Decoding to Mitigate the Effects of Pulse-Noise Interference

    DTIC Science & Technology

    2006-12-01

    when the signal is transmitted over a frequency-selective, slowly fading Nakagami channel in a pulse-noise interference environment when errors-and...conditions when pulse-noise interference is present. 15. NUMBER OF PAGES 125 14. SUBJECT TERMS IEEE 802.11g WLAN Standard, Nakagami Fading...selective, slowly fading Nakagami channel in a pulse-noise interference environment when errors-and-erasures Viterbi decoding is used is examined. The

  4. Ultrasound window-modulated compounding Nakagami imaging: Resolution improvement and computational acceleration for liver characterization.

    PubMed

    Ma, Hsiang-Yang; Lin, Ying-Hsiu; Wang, Chiao-Yin; Chen, Chiung-Nien; Ho, Ming-Chih; Tsui, Po-Hsiang

    2016-08-01

    Ultrasound Nakagami imaging is an attractive method for visualizing changes in envelope statistics. Window-modulated compounding (WMC) Nakagami imaging was reported to improve image smoothness. The sliding window technique is typically used for constructing ultrasound parametric and Nakagami images. Using a large window overlap ratio may improve the WMC Nakagami image resolution but reduces computational efficiency. Therefore, the objectives of this study include: (i) exploring the effects of the window overlap ratio on the resolution and smoothness of WMC Nakagami images; (ii) proposing a fast algorithm that is based on the convolution operator (FACO) to accelerate WMC Nakagami imaging. Computer simulations and preliminary clinical tests on liver fibrosis samples (n=48) were performed to validate the FACO-based WMC Nakagami imaging. The results demonstrated that the width of the autocorrelation function and the parameter distribution of the WMC Nakagami image reduce with the increase in the window overlap ratio. One-pixel shifting (i.e., sliding the window on the image data in steps of one pixel for parametric imaging) as the maximum overlap ratio significantly improves the WMC Nakagami image quality. Concurrently, the proposed FACO method combined with a computational platform that optimizes the matrix computation can accelerate WMC Nakagami imaging, allowing the detection of liver fibrosis-induced changes in envelope statistics. FACO-accelerated WMC Nakagami imaging is a new-generation Nakagami imaging technique with an improved image quality and fast computation.

  5. Using ultrasound Nakagami imaging to assess liver fibrosis in rats.

    PubMed

    Ho, Ming-Chih; Lin, Jen-Jen; Shu, Yu-Chen; Chen, Chiung-Nien; Chang, King-Jen; Chang, Chien-Cheng; Tsui, Po-Hsiang

    2012-02-01

    This study explored the feasibility of using the ultrasound Nakagami image to assess the degree of liver fibrosis in rats. The rat has been widely used as a model in investigations of liver fibrosis. Ultrasound grayscale imaging makes it possible to observe fibrotic rat livers in real time. Statistical analysis of the envelopes of signals backscattered from rat livers may provide useful clues about the degree of liver fibrosis. The Nakagami-model-based image has been shown to be useful for characterizing scatterers in tissues by reflecting the echo statistics, and hence the Nakagami image may serve as a functional imaging tool for quantifying rat liver fibrosis. To validate this idea, fibrosis was induced in each rat liver (n=21) by an intraperitoneal injection of 0.5% dimethylnitrosamine. Livers were excised from rats for in vitro ultrasound scanning using a single-element transducer. The backscattered-signal envelopes of the acquired raw ultrasound signals were used for Nakagami imaging. The Metavir score determined by a pathologist was used to histologically quantify the degree of liver fibrosis. It was found that the Nakagami image could be used to distinguish different degrees of liver fibrosis in rats, since the average Nakagami parameter increased from 0.55 to 0.83 as the fibrosis score increased from 0 (i.e., normal) to 4. This correlation may be due to liver fibrosis in rats involving an increase in the concentration of local scatterers and the appearance of the periodic structures or clustering of scatterers that would change the backscattering statistics. The current findings indicate that the ultrasound Nakagami image has great potential as a functional imaging tool to complement the use of the conventional B-scan in animal studies of liver fibrosis.

  6. 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.

  7. Effect of adaptive threshold filtering on ultrasonic nakagami parameter to detect variation in scatterer concentration.

    PubMed

    Tsui, Po-Hsiang; Wan, Yung-Liang; Huang, Chih-Chung; Wang, Ming-Chen

    2010-10-01

    The Nakagami parameter is associated with the Nakagami distribution estimated from ultrasonic backscattered signals and closely reflects the scatterer concentrations in tissues. There is an interest in exploring the possibility of enhancing the ability of the Nakagami parameter to characterize tissues. In this paper, we explore the effect of adaptive thresholdfiltering based on the noise-assisted empirical mode decomposition of the ultrasonic backscattered signals on the Nakagami parameter as a function of scatterer concentration for improving the Nakagami parameter performance. We carried out phantom experiments using 5 MHz focused and nonfocused transducers. Before filtering, the dynamic ranges of the Nakagami parameter, estimated using focused and nonfocused transducers between the scatterer concentrations of 2 and 32 scatterers/mm3, were 0.44 and 0.1, respectively. After filtering, the dynamic ranges of the Nakagami parameter, using the focused and nonfocused transducers, were 0.71 and 0.79, respectively. The experimental results showed that the adaptive threshold filter makes the Nakagami parameter measured by a focused transducer more sensitive to the variation in the scatterer concentration. The proposed method also endows the Nakagami parameter measured by a nonfocused transducer with the ability to differentiate various scatterer concentrations. However, the Nakagami parameters estimated by focused and nonfocused transducers after adaptive threshold filtering have different physical meanings: the former represents the statistics of signals backscattered from unresolvable scatterers while the latter is associated with stronger resolvable scatterers or local inhomogeneity due to scatterer aggregation.

  8. 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

  9. 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

    2016-09-08

    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.

  10. Ultrasonic backscattering in tissue: characterization through Nakagami-generalized inverse Gaussian distribution.

    PubMed

    Agrawal, Rajeev; Karmeshu

    2007-02-01

    Ultrasonic tissue characterization through composite probability distributions such as Nakagami-lognormal, Nakagami-gamma, Nakagami-inverse Gaussian has been found to be useful. Such a probabilistic description also depicts heavy tails which arise from multiple scattering in tissue besides local and global variations in scattering cross-sections. A new composite probability distribution, viz. Nakagami-generalized inverse Gaussian distribution (NGIGD) with four parameters is proposed which under different limiting conditions results in approximating the known distributions. A salient aspect of the new distribution is that the probability density function (pdf) of NGIGD variate is available in closed form and is analytically tractable.

  11. Development of a heterogeneous microwave network fade simulation tool applicable to networks that span Europe

    NASA Astrophysics Data System (ADS)

    Paulson, Kevin S.; Basarudin, Hafiz

    2011-08-01

    Several research groups in Europe are developing joint channel simulators for arbitrarily complex networks of terrestrial and slant path, microwave telecommunications links. Currently, the Hull Rain Fade Network Simulator (HRFNS) developed at University of Hull can simulate rain fade on arbitrary terrestrial networks in the southern United Kingdom, producing joint rain fade time series with a 10 s integration time. This paper reports on work to broaden the function of the existing HRFNS to include slant paths such as Earth-space links and communications to high altitude platforms and unmanned airborne systems. The area of application of the new simulation tool is being extended to the whole of Europe, and other fade mechanisms are being included. Nimrod/OPERA has been chosen as the input meteorological data sets for the new system to simulate rain fade. Zero-degree isotherm heights taken from NCEP/NCAR Reanalysis Data are used in conjunction with the Eden-Bacon sleet (wet snow) model to introduce melting layer effects. Other fading mechanisms, including cloud fade, scintillation and absorption losses by atmospheric gasses, can be added to the simulator. The simulator is tested against ITU-R models for rain fade distribution experienced by terrestrial and Earth-space links in the southern United Kingdom. Statistics of fade dynamics, i.e., fade slope and fade duration, for a simulated Earth-space link are compared to International Telecommunication Union models.

  12. Microvascular flow estimation by microbubble-assisted Nakagami imaging.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng

    2009-04-01

    The destruction and replenishment of microbubbles has been previously applied to estimating blood flow in the microcirculation. The rate of increase of the time-intensity curve (TIC) due to microbubbles flowing into the region-of-interest (ROI) as measured from the conventional B-mode images reflects the flow velocity. In this study, we monitored microbubble replenishment using a new proposed approach called the time-Nakagami-parameter curve (TNC) obtained from the parametric image based on the Nakagami statistical parameter for quantifying the microvascular flow velocity. The Nakagami parameter is estimated from signal envelope to reflect the backscattered statistics. The feasibility of using the TNC to estimate the microvascular flow was explored by carrying out phantom measurements and in vivo animal experiments. The rates of increase of the TIC and TNC were quantified as the rate constants beta(I) and beta(N) of monoexponential fitted curves, respectively. The experimental results showed that beta(N) behaves similarly to the conventional beta(I) in quantifying the flow velocity. Moreover, the tolerance to the effects of clutter is greater for the TNC than for the TIC, which makes it possible to use beta(N) to differentiate various flow velocities even when the ROI contains nonperfused areas. This finding suggests that the TNC-based technique can be used as a complementary tool for the conventional TIC to improve measurement of blood flow in the microcirculation.

  13. Use of nakagami statistics and empirical mode decomposition for ultrasound tissue characterization by a nonfocused transducer.

    PubMed

    Tsui, Po-Hsiang; Chang, Chien-Cheng; Ho, Ming-Chih; Lee, Yu-Hsin; Chen, Yung-Sheng; Chang, Chien-Chung; Huang, Norden E; Wu, Zhao-Hua; Chang, King-Jen

    2009-12-01

    The Nakagami parameter associated with the Nakagami distribution estimated from ultrasonic backscattered signals reflects the scatterer concentration in a tissue. A nonfocused transducer does not allow tissue characterization based on the Nakagami parameter. This paper proposes a new method called the noise-assisted Nakagami parameter based on empirical mode decomposition of noisy backscattered echoes to allow quantification of the scatterer concentration based on data obtained using a nonfocused transducer. To explore the practical feasibility of the proposed method, the current study performed experiments on phantoms and measurements on rat livers in vitro with and without fibrosis induction. The results show that using a nonfocused transducer makes it possible to use the noise-assisted Nakagami parameter to classify phantoms with different scatterer concentrations and different stages of liver fibrosis in rats more accurately than when using techniques based on the echo intensity and the conventional Nakagami parameter. However, the conventional Nakagami parameter and the noise-assisted Nakagami parameter have different meanings: the former represents the statistics of signals backscattered from unresolvable scatterers, whereas the latter is associated with stronger resolvable scatterers or local inhomogeneity caused by scatterer aggregation.

  14. 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.

  15. Noise-assisted correlation algorithm for suppressing noise-induced artifacts in ultrasonic Nakagami images.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Huang, Chih-Chung

    2012-05-01

    Ultrasonic Nakagami images can complement conventional B-mode images for scatterer characterization. White noise in anechoic areas leads to artifacts that affect the Nakagami image to characterize tissues. Artifact removal requires rejection of the white noise without deforming the backscattered waveform. This study proposes a noise-assisted correlation algorithm (NCA) and carries out simulations, phantom experiments, and clinical measurements to validate its feasibility and practicality. The simulation results show that the NCA can reject white noise in an anechoic area without any deformation of the backscattered waveforms. The results obtained from phantoms and tissues further demonstrate that the proposed NCA can suppress a Nakagami image artifact without changing the texture of the Nakagami image of the scattering background. The NCA is an essential algorithm to construct artifact-free Nakagami image for correctly reflecting scatterer properties of biological tissues.

  16. 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.

  17. Digital Communications in Fading Channels: COMLINK Validation

    DTIC Science & Technology

    2000-09-01

    U.S. Customary to metric (SI) units of measurement MULTIPLY "- BY D- TOGET TOGET N-o BY -- DIVIDE angstrom 1.000000 x E -10 meters (m) atmosphere...normal) 1.01325 x E +2 kilo pascal (kPa) bar 1.000000 x E +2 kilo pascal (kPa) barn 1.000000 x E -28 meter2 (m2 ) British thermal unit (thermochemical...1.054350 x E +3 joule (J) calorie (thermochemical) 4.184000 joule (J) cal (thermochemical) /cm2’ 4.184000 x E -2 mega joule/m2 (MJ/m 2) curie 3.700000

  18. Feasibility of using Nakagami distribution in evaluating the formation of ultrasound-induced thermal lesions.

    PubMed

    Zhang, Siyuan; Zhou, Fanyu; Wan, Mingxi; Wei, Min; Fu, Quanyou; Wang, Xing; Wang, Supin

    2012-06-01

    The acoustic posterior shadowing effects of bubbles influence the accuracy for defining the location and range of ablated thermal lesions during focused ultrasound surgery when using ultrasonic monitoring imaging. This paper explored the feasibility of using Nakagami distribution to evaluate the ablated region induced by focused ultrasound exposures at different acoustic power levels in transparent tissue-mimicking phantoms. The mean value of the Nakagami parameter m was about 0.5 in the cavitation region and increased to around 1 in the ablated region. Nakagami images were not subject to significant shadowing effects of bubbles. Ultrasound-induced thermal lesions observed in the photos and Nakagami images were overshadowed by bubbles in the B-mode images. The lesion size predicted in the Nakagami images was smaller than that predicted in the photos due to the sub resolvable effect of Nakagami imaging at the interface. This preliminary study on tissue-mimicking phantom suggested that the Nakagami parameter m may have the potential use in evaluating the formation of ultrasound-induced thermal lesion when the shadowing effect of bubbles is strong while the thermal lesion was small. Further studies in vivo and in vitro will be needed to evaluate the potential application.

  19. Ultrasonic Nakagami imaging: a strategy to visualize the scatterer properties of benign and malignant breast tumors.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Liao, Yin-Yin; Chang, Chien-Cheng; Kuo, Wen-Hung; Chang, King-Jen; Chen, Chiung-Nien

    2010-02-01

    Previous studies have demonstrated the usefulness of the Nakagami parameter in characterizing breast tumors by ultrasound. However, physicians or radiologists may need imaging tools in a clinical setting to visually identify the properties of breast tumors. This study proposed the ultrasonic Nakagami image to visualize the scatterer properties of breast tumors and then explored its clinical performance in classifying benign and malignant tumors. Raw data of ultrasonic backscattered signals were collected from 100 patients (50 benign and 50 malignant cases) using a commercial ultrasound scanner with a 7.5 MHz linear array transducer. The backscattered signals were used to form the B-scan and the Nakagami images of breast tumors. For each tumor, the average Nakagami parameter was calculated from the pixel values in the region-of-interest in the Nakagami image. The receiver operating characteristic (ROC) curve was used to evaluate the clinical performance of the Nakagami image. The results showed that the Nakagami image shadings in benign tumors were different from those in malignant cases. The average Nakagami parameters for benign and malignant tumors were 0.69 +/- 0.12 and 0.55 +/- 0.12, respectively. This means that the backscattered signals received from malignant tumors tend to be more pre-Rayleigh distributed than those from benign tumors, corresponding to a more complex scatterer arrangement or composition. The ROC analysis showed that the area under the ROC curve was 0.81 +/- 0.04 and the diagnostic accuracy was 82%, sensitivity was 92% and specificity was 72%. The results showed that the Nakagami image is useful to distinguishing between benign and malignant breast tumors.

  20. Tissue Characterization on Ultrasound Harmonic Signals using Nakagami Statistics

    NASA Astrophysics Data System (ADS)

    Lin, Fanglue; Cristea, Anca; Cachard, Christian; Basset, Olivier

    Quantitative ultrasound (QUS) imaging provides a way to characterize biological tissue. The QUS estimates can be obtained from the envelope statistics. Previous studies are mainly based on the whole backscattered signals analysis. However, the ultrasound propagation is a nonlinear process and the harmonic signals can therefore reveal the nonlinear nature of a biological medium. The present study investigates the statistics of harmonic signal envelopes to relate the distribution parameters to the nonlinear coefficients. The main results demonstrate that the distributions exhibit a different behavior for fundamental and harmonic signals and that media with different nonlinearities can be distinguished, when using Nakagami statistics on the harmonic signal envelopes.

  1. Study of ultrasonic echo envelope based on Nakagami-inverse Gaussian distribution.

    PubMed

    Karmeshu; Agrawal, Rajeev

    2006-03-01

    A new probability density function (pdf) to describe the envelope of the backscattered echoes from tissues is proposed. The combined effect of multiple scattering and randomness arising from local and global variations in scattering cross-section is captured through Nakagami-inverse Gaussian distribution (NIGD). The proposed distribution has the advantage that it has a closed form unlike the realistic Nakagami-lognormal distribution (NLD). The degree of closeness, as measured in terms of Kullback-Leibler (KL) distance between two probability distributions is computed. It is shown that NIGD much more closely approximates NLD compared to Nakagami-gamma distribution (NGD) used to model such problems.

  2. Phase and frequency coherency in fading environment in tracking and data relay satellites

    NASA Astrophysics Data System (ADS)

    Varanasi, S.; Gupta, S. C.

    Communication systems employing relay satellites require strict maintaining of frequency and phase coherence. In this paper, the tracking performance of a Digital Fading Phase Locked Loop (DFPLL) is presented considering that the transmitted signal passes through a Rician fading communication channel and also an Additive White Gaussian Noise (AWGN) channel. The stochastic difference equations governing the loop operation considering both phase-step and frequency-step inputs for a first order DFPLL is derived and also mathematical modeling of the Rician fading communication channel. Approximate analytic expressions for the steady state phase error process probability density function (pdf) and phase error variance, which characterize the tracking performance of the loop are presented by solving the corresponding Chapman-Kolmogorov (C-K) equations for both types of inputs considered. Numerical and simulation results are provided that confirm the analytical results for various signal to noise ratios and for various values of the fading parameter.

  3. Locally adaptive Nakagami-based ultrasound similarity measures.

    PubMed

    Wachinger, Christian; Klein, Tassilo; Navab, Nassir

    2012-04-01

    The derivation of statistically optimal similarity measures for intensity-based registration is possible by modeling the underlying image noise distribution. The parameters of these distributions are, however, commonly set heuristically across all images. In this article, we show that the estimation of the parameters on the present images largely improves the registration, which is a consequence of the more accurate characterization of the image noise. More precisely, instead of having constant parameters over the entire image domain, we estimate them on patches, leading to a local adaptation of the similarity measure. While this basic idea of creating locally adaptive metrics is interesting for various fields of application, we present the derivation for ultrasound imaging. The domain of ultrasound is particularly appealing for this approach, due to the inherent contamination with speckle noise. Furthermore, there exist detailed analyses of suitable noise distributions in the literature. We present experiments for applying a bivariate Nakagami distribution that facilitates modeling of several scattering scenarios prominent in medical ultrasound. Depending on the number of scatterers per resolution cell and the presence of coherent structures, different Nakagami parameters are required to obtain a valid approximation of the intensity statistics and to account for distributional locality. Our registration results on radio-frequency ultrasound data confirm the theoretical necessity for a spatial adaptation of similarity metrics.

  4. Classification of breast masses by ultrasonic Nakagami imaging: a feasibility study.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng; Liao, Yin-Yin

    2008-11-07

    Ultrasound is an important clinical tool in noninvasive diagnoses of breast cancer. The Nakagami statistical parameter estimated from the ultrasonic backscattered envelope has been demonstrated to be useful in complementing conventional B-mode scans when classifying breast masses. However, the shadowing effect caused by certain high-attenuation tumors in the B-mode image makes the tumor contour unclear, and thus it is more difficult to choose an appropriate region of interest from which to collect tumor data for estimating the Nakagami parameter. This study explored the feasibility of using the Nakagami parametric image to overcome the shadowing effect for visualizing the properties of breast masses. Experiments were performed on a breast-mimicking phantom and on some typical clinical cases for cysts, fat and tumors (fibroadenoma) (n = 18) in order to explore the performance of the Nakagami image under ideal and practical conditions. The experimental results showed that the Nakagami image pixels (i.e. the local Nakagami parameter) in the cyst, tumor and fat are 0.21 +/- 0.01, 0.65 +/- 0.05 and 0.98 +/- 0.07, respectively, for six independent phantom measurements, and 0.14 +/- 0.03, 0.67 +/- 0.11 and 0.89 +/- 0.08, respectively, for clinical experiments. This suggests that the Nakagami image is able to classify various breast masses (p < 0.005) although the clinical results from tumors of different cases have a larger variance that may be caused by the complexity of real breast tissues. In particular, unlike the B-mode image, the Nakagami image is not subject to significant shadowing effects, making it useful to complement the B-mode image to describe the tumor contour for identifying the tumor-related region when the shadowing effect is stronger or a low system gain is used.

  5. Classification of breast masses by ultrasonic Nakagami imaging: a feasibility study

    NASA Astrophysics Data System (ADS)

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng; Liao, Yin-Yin

    2008-11-01

    Ultrasound is an important clinical tool in noninvasive diagnoses of breast cancer. The Nakagami statistical parameter estimated from the ultrasonic backscattered envelope has been demonstrated to be useful in complementing conventional B-mode scans when classifying breast masses. However, the shadowing effect caused by certain high-attenuation tumors in the B-mode image makes the tumor contour unclear, and thus it is more difficult to choose an appropriate region of interest from which to collect tumor data for estimating the Nakagami parameter. This study explored the feasibility of using the Nakagami parametric image to overcome the shadowing effect for visualizing the properties of breast masses. Experiments were performed on a breast-mimicking phantom and on some typical clinical cases for cysts, fat and tumors (fibroadenoma) (n = 18) in order to explore the performance of the Nakagami image under ideal and practical conditions. The experimental results showed that the Nakagami image pixels (i.e. the local Nakagami parameter) in the cyst, tumor and fat are 0.21 ± 0.01, 0.65 ± 0.05 and 0.98 ± 0.07, respectively, for six independent phantom measurements, and 0.14 ± 0.03, 0.67 ± 0.11 and 0.89 ± 0.08, respectively, for clinical experiments. This suggests that the Nakagami image is able to classify various breast masses (p < 0.005) although the clinical results from tumors of different cases have a larger variance that may be caused by the complexity of real breast tissues. In particular, unlike the B-mode image, the Nakagami image is not subject to significant shadowing effects, making it useful to complement the B-mode image to describe the tumor contour for identifying the tumor-related region when the shadowing effect is stronger or a low system gain is used.

  6. 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.

  7. 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…

  8. Differential Space-Time Modulation for Wideband Wireless Networks

    DTIC Science & Technology

    2006-09-30

    modulation for wireless relay networks in Nakagami -m channels,” in Proceedings of the 2006 IEEE International Conference on Acoustic, Speech, and Signal... Nakagami -m fading channels," in Proceedings of the 6th IEEE International Workshop on Signal Processing Advances for Wireless Communications (SPAWC

  9. An introduction to Doppler effect and fading in mobile communications

    NASA Astrophysics Data System (ADS)

    Depaula, Abdon B.

    1992-12-01

    In this research we present an introductory analysis of a complex aspect of mobile communications: Doppler effect is evaluated in both Ricean and Rayleigh channels. A noncoherent 2-FSK scheme is selected to evaluate the behavior of the system under very strong fading channel conditions. The analysis is conducted for the binary case due to the possibility of developing closed form solutions. Therefore, the approach is simplified avoiding long lasting simulations that may obscure the concepts. The probability of bit error for the 2-FSK case can also be used as an initial bound for a M-FSK scheme. Diversity is evaluated as a means of combating fading and Doppler effects. Error correcting codes, in the form of a convolutional codes, are also used and applied to both effects.

  10. 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

  11. Fading testbed for free-space optical communications

    NASA Astrophysics Data System (ADS)

    Shrestha, Amita; Giggenbach, Dirk; Mustafa, Ahmad; Pacheco-Labrador, Jorge; Ramirez, Julio; Rein, Fabian

    2016-10-01

    Free-space optical (FSO) communication is a very attractive technology offering very high throughput without spectral regulation constraints, yet allowing small antennas (telescopes) and tap-proof communication. However, the transmitted signal has to travel through the atmosphere where it gets influenced by atmospheric turbulence, causing scintillation of the received signal. In addition, climatic effects like fogs, clouds and rain also affect the signal significantly. Moreover, FSO being a line of sight communication requires precise pointing and tracking of the telescopes, which otherwise also causes fading. To achieve error-free transmission, various mitigation techniques like aperture averaging, adaptive optics, transmitter diversity, sophisticated coding and modulation schemes are being investigated and implemented. Evaluating the performance of such systems under controlled conditions is very difficult in field trials since the atmospheric situation constantly changes, and the target scenario (e.g. on aircraft or satellites) is not easily accessible for test purposes. Therefore, with the motivation to be able to test and verify a system under laboratory conditions, DLR has developed a fading testbed that can emulate most realistic channel conditions. The main principle of the fading testbed is to control the input current of a variable optical attenuator such that it attenuates the incoming signal according to the loaded power vector. The sampling frequency and mean power of the vector can be optionally changed according to requirements. This paper provides a brief introduction to software and hardware development of the fading testbed and measurement results showing its accuracy and application scenarios.

  12. 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.

  13. Feasibility of Using Ultrasonic Nakagami Imaging for Monitoring Microwave-Induced Thermal Lesion in Ex Vivo Porcine Liver.

    PubMed

    Zhang, Siyuan; Han, Yuqiang; Zhu, Xingguang; Shang, Shaoqiang; Huang, Guojing; Zhang, Lei; Niu, Gang; Wang, Supin; He, Xijing; Wan, Mingxi

    2017-02-01

    The feasibility of using ultrasonic Nakagami imaging to evaluate thermal lesions induced by microwave ablation (MWA) in ex vivo porcine liver was explored. Dynamic changes in echo amplitudes and Nakagami parameters in the region of the MWA-induced thermal lesion, as well as the contrast-to-noise ratio (CNR) between the MWA-induced thermal lesion and the surrounding normal tissue, were calculated simultaneously during the MWA procedure. After MWA exposure, a bright hyper-echoic region appeared in ultrasonic B-mode and Nakagami parameter images as an indicator of the thermal lesion. Mean values of the Nakagami parameter in the thermal lesion region increased to 0.58, 0.71 and 0.91 after 1, 3 and 5 min of MVA. There were no significant differences in envelope amplitudes in the thermal lesion region among ultrasonic B-mode images obtained after different durations of MWA. Unlike ultrasonic B-mode images, Nakagami images were less affected by the shadow effect in monitoring of MWA exposure, and a fairly complete hyper-echoic region was observed in the Nakagami image. The mean value of the Nakagami parameter increased from approximately 0.47 to 0.82 during MWA exposure. At the end of the postablation stage, the mean value of the Nakagami parameter decreased to 0.55 and was higher than that before MWA exposure. CNR values calculated for Nakagami parameter images increased from 0.13 to approximately 0.61 during MWA and then decreased to 0.26 at the end of the post-ablation stage. The corresponding CNR values calculated for ultrasonic B-mode images were 0.24, 0.42 and 0.17. This preliminary study on ex vivo porcine liver suggested that Nakagami imaging have potential use in evaluating the formation of MWA-induced thermal lesions. Further in vivo studies are needed to evaluate the potential application.

  14. 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.}

  15. Linear and nonlinear characterization of microbubbles and tissue using the Nakagami statistical model.

    PubMed

    Bahbah, N; Novell, A; Bouakaz, A; Djelouah, H

    2017-04-01

    The goal of this work is to exploit the statistical signatures for discrimination between biological tissues and contrast microbubbles in order to develop new strategies for contrast imaging and tissue characterization. For this purpose, the efficiency of the Nakagami statistical model, for describing the ultrasonic echoes of both contrast microbubbles and tissues, was investigated. Experimental measurements have been performed using a linear array probe connected to an open research platform. A commercially available in vitro phantom was used to mimic biological tissue in which SonoVue contrast microbubbles were flowing. Experimental ultrasound echoes have been filtered around the transmitted frequency (fundamental at 2.5MHz) and around twice the transmitted frequency (at 5MHz) for 2nd harmonic analysis, and a logarithmic compression was applied. The signals have been analyzed in order to evaluate the Nakagami parameter m, the scaling parameter Ω and the probability density function at both frequencies. Parametric images based on the Nakagami parameters map (Nakagami-mode images) were reconstructed and compared to B-mode images. Contrary to the B-mode image which is influenced by the system settings and user operations, the Nakagami parametric image is only based on the backscattered statistics of the ultrasonic signals in a local phantom. Such an imaging principle allows the Nakagami image to quantify the local scatterer concentrations in the phantom and to extract the backscattering information from the regions of the weakest echoes that may be lost in the conventional B-mode image. Results show that the tissue and microbubbles characterization is more sensitive in the 2nd harmonic mode when a logarithmic transform is used. These results would be useful for improving the ultrasound image quality and contrast detection in nonlinear mode.

  16. Tight Bounds on the Ergodic Capacity of Cooperative Analog Relaying with Adaptive Source Transmission Techniques

    DTIC Science & Technology

    2010-05-01

    limited to Rayleigh fading. But in an airborne platform, it is much more reasonable to model the channel gain of each link as a Nakagami -m or a Rice...link SNR, and 2 2 , , , ,(1/ 1/ ) 2 (1/ 1/ )s i i d s i i ds sΔ = Ω − Ω + Ω + Ω + Moreover, the MGF of iγ for a Nakagami channel...8) 2 If a closed-form expression for iγ is not available (e.g., Nakagami -m channel with i.n.d fading statistics), but does exist for

  17. Monitoring radiofrequency ablation using real-time ultrasound Nakagami imaging combined with frequency and temporal compounding techniques.

    PubMed

    Zhou, Zhuhuang; Wu, Shuicai; Wang, Chiao-Yin; Ma, Hsiang-Yang; Lin, Chung-Chih; Tsui, Po-Hsiang

    2015-01-01

    Gas bubbles induced during the radiofrequency ablation (RFA) of tissues can affect the detection of ablation zones (necrosis zone or thermal lesion) during ultrasound elastography. To resolve this problem, our previous study proposed ultrasound Nakagami imaging for detecting thermal-induced bubble formation to evaluate ablation zones. To prepare for future applications, this study (i) created a novel algorithmic scheme based on the frequency and temporal compounding of Nakagami imaging for enhanced ablation zone visualization, (ii) integrated the proposed algorithm into a clinical scanner to develop a real-time Nakagami imaging system for monitoring RFA, and (iii) investigated the applicability of Nakagami imaging to various types of tissues. The performance of the real-time Nakagami imaging system in visualizing RFA-induced ablation zones was validated by measuring porcine liver (n = 18) and muscle tissues (n = 6). The experimental results showed that the proposed algorithm can operate on a standard clinical ultrasound scanner to monitor RFA in real time. The Nakagami imaging system effectively monitors RFA-induced ablation zones in liver tissues. However, because tissue properties differ, the system cannot visualize ablation zones in muscle fibers. In the future, real-time Nakagami imaging should be focused on the RFA of the liver and is suggested as an alternative monitoring tool when advanced elastography is unavailable or substantial bubbles exist in the ablation zone.

  18. Detecting changes in ultrasound backscattered statistics by using Nakagami parameters: Comparisons of moment-based and maximum likelihood estimators.

    PubMed

    Lin, Jen-Jen; Cheng, Jung-Yu; Huang, Li-Fei; Lin, Ying-Hsiu; Wan, Yung-Liang; Tsui, Po-Hsiang

    2017-05-01

    The Nakagami distribution is an approximation useful to the statistics of ultrasound backscattered signals for tissue characterization. Various estimators may affect the Nakagami parameter in the detection of changes in backscattered statistics. In particular, the moment-based estimator (MBE) and maximum likelihood estimator (MLE) are two primary methods used to estimate the Nakagami parameters of ultrasound signals. This study explored the effects of the MBE and different MLE approximations on Nakagami parameter estimations. Ultrasound backscattered signals of different scatterer number densities were generated using a simulation model, and phantom experiments and measurements of human liver tissues were also conducted to acquire real backscattered echoes. Envelope signals were employed to estimate the Nakagami parameters by using the MBE, first- and second-order approximations of MLE (MLE1 and MLE2, respectively), and Greenwood approximation (MLEgw) for comparisons. The simulation results demonstrated that, compared with the MBE and MLE1, the MLE2 and MLEgw enabled more stable parameter estimations with small sample sizes. Notably, the required data length of the envelope signal was 3.6 times the pulse length. The phantom and tissue measurement results also showed that the Nakagami parameters estimated using the MLE2 and MLEgw could simultaneously differentiate various scatterer concentrations with lower standard deviations and reliably reflect physical meanings associated with the backscattered statistics. Therefore, the MLE2 and MLEgw are suggested as estimators for the development of Nakagami-based methodologies for ultrasound tissue characterization.

  19. Monitoring Radiofrequency Ablation Using Real-Time Ultrasound Nakagami Imaging Combined with Frequency and Temporal Compounding Techniques

    PubMed Central

    Zhou, Zhuhuang; Wu, Shuicai; Wang, Chiao-Yin; Ma, Hsiang-Yang; Lin, Chung-Chih; Tsui, Po-Hsiang

    2015-01-01

    Gas bubbles induced during the radiofrequency ablation (RFA) of tissues can affect the detection of ablation zones (necrosis zone or thermal lesion) during ultrasound elastography. To resolve this problem, our previous study proposed ultrasound Nakagami imaging for detecting thermal-induced bubble formation to evaluate ablation zones. To prepare for future applications, this study (i) created a novel algorithmic scheme based on the frequency and temporal compounding of Nakagami imaging for enhanced ablation zone visualization, (ii) integrated the proposed algorithm into a clinical scanner to develop a real-time Nakagami imaging system for monitoring RFA, and (iii) investigated the applicability of Nakagami imaging to various types of tissues. The performance of the real-time Nakagami imaging system in visualizing RFA-induced ablation zones was validated by measuring porcine liver (n = 18) and muscle tissues (n = 6). The experimental results showed that the proposed algorithm can operate on a standard clinical ultrasound scanner to monitor RFA in real time. The Nakagami imaging system effectively monitors RFA-induced ablation zones in liver tissues. However, because tissue properties differ, the system cannot visualize ablation zones in muscle fibers. In the future, real-time Nakagami imaging should be focused on the RFA of the liver and is suggested as an alternative monitoring tool when advanced elastography is unavailable or substantial bubbles exist in the ablation zone. PMID:25658424

  20. 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…

  1. Minimum requirement of artificial noise level for using noise-assisted correlation algorithm to suppress artifacts in ultrasonic Nakagami images.

    PubMed

    Tsui, Po-Hsiang

    2012-04-01

    The Nakagami image is a complementary imaging mode for pulse-echo ultrasound B-scan to characterize tissues. White noise in anechoic areas induces artifacts in the Nakagami image. Recently, we proposed a noise-assisted correlation algorithm (NCA) for suppressing the Nakagami artifact. In the NCA, artificial white noise is intentionally added twice to backscattered signals to produce two noisy data, which are used to establish a correlation profile for rejecting noise. This study explored the effects of artificial noise level on the NCA to suppress the artifact of the Nakagami image. Simulations were conducted to produce B-mode images of anechoic regions under signal-to-noise ratios (SNRs) of 20, 10 and 5 dB. Various artificial noise levels ranging from 0.1- to 1-fold of the intrinsic noise amplitude were used in the NCA for constructing the Nakagami images. Phantom experiments were conducted to validate the performance of using the optimal artificial noise level suggested by the simulation results to suppress the Nakagami artifacts by the NCA. The simulation results indicated that the artifacts of the Nakagami image in the anechoic regions can be gradually suppressed by increasing the artificial noise level used in the NCA to improve the image contrast-to-noise ratio (CNR). The CNR of the Nakagami image reached 20 dB when the artificial noise level was 0.7-fold of the intrinsic noise amplitude. This criterion was demonstrated by the phantom results to provide the NCA with an excellent ability to obtain artifact-free Nakagami images.

  2. 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.

  3. Performance Analysis of Dual-hop MIMO Relay Systems with MRT&RAS in the Presence of Co-channel Interference

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoming; Cai, Yueming; Yang, Weiwei

    2013-09-01

    This paper focuses on the downlink dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay systems that employ the maximal-ratio transmission and receive antenna selection scheme (MRT&RAS) for use in each hop. The system under consideration is equipped with arbitrary NS, NR, and ND antennas at the base station (BS), relay station (RS), and mobile station (MS), respectively. The system performance has been investigated over Nakagami-m fading in presence of independent but not necessarily identically distributed co-channel interferences (CCIs) at both the RS and MS. First, we derive an accurate closed-form approximate expression for the outage probability and a single-integral expression for the average symbol error rate (SER), respectively. Besides, to render direct insights into the combined effect of multiple-antenna and interference on the system performance, the asymptotic expressions for the outage probability and the average SER are also presented. Furthermore, we determine the optimal power allocation (OPA) by using the exact and asymptotic methods, respectively, such that the outage probability is minimized. Finally, numerical results validate the correctness of the derived expressions and show that OPA offers superior performance over uniform power allocation. Our analysis and results provide insights on investigating and optimizing the performance of the downlink MIMO relay transmission in practical interference-limited wireless networks.

  4. Differential reinforcement with and without instructional fading.

    PubMed Central

    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. PMID:12365743

  5. Feasibility study of using high-frequency ultrasonic Nakagami imaging for characterizing the cataract lens in vitro.

    PubMed

    Tsui, Po-Hsiang; Huang, Chih-Chung; Chang, Chien-Cheng; Wang, Shyh-Hau; Shung, K Kirk

    2007-11-07

    A cataract is a clouding of the crystalline lens that reduces the amount of incoming light and impairs visual perception. Phacoemulsification is the most common surgical method for treating advanced cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the feasibility of using an ultrasonic parametric image based on the Nakagami distribution to quantify the lens hardness. Young's modulus was measured in porcine lenses in which cataracts had been artificially induced. High-frequency ultrasound at 35 MHz was used to obtain the B-mode and Nakagami images of the cataract lenses. The averaged integrated backscatter and Nakagami parameters were also estimated in the region of interest. The experimental results show that the conventional B-scan and integrated backscatter are inadequate for quantifying the lens hardness, whereas Nakagami imaging allows different degrees of lens hardening to be distinguished both globally and locally based on the concentration of fiber coemption therein.

  6. Feasibility study of using high-frequency ultrasonic Nakagami imaging for characterizing the cataract lens in vitro

    NASA Astrophysics Data System (ADS)

    Tsui, Po-Hsiang; Huang, Chih-Chung; Chang, Chien-Cheng; Wang, Shyh-Hau; Shung, K. Kirk

    2007-11-01

    A cataract is a clouding of the crystalline lens that reduces the amount of incoming light and impairs visual perception. Phacoemulsification is the most common surgical method for treating advanced cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the feasibility of using an ultrasonic parametric image based on the Nakagami distribution to quantify the lens hardness. Young's modulus was measured in porcine lenses in which cataracts had been artificially induced. High-frequency ultrasound at 35 MHz was used to obtain the B-mode and Nakagami images of the cataract lenses. The averaged integrated backscatter and Nakagami parameters were also estimated in the region of interest. The experimental results show that the conventional B-scan and integrated backscatter are inadequate for quantifying the lens hardness, whereas Nakagami imaging allows different degrees of lens hardening to be distinguished both globally and locally based on the concentration of fiber coemption therein.

  7. Artifact reduction of ultrasound Nakagami imaging by combining multifocus image reconstruction and the noise-assisted correlation algorithm.

    PubMed

    Tsui, Po-Hsiang; Tsai, Yu-Wei

    2015-01-01

    Several studies have investigated Nakagami imaging to complement the B-scan in tissue characterization. The noise-induced artifact and the parameter ambiguity effect can affect performance of Nakagami imaging in the detection of variations in scatterer concentration. This study combined multifocus image reconstruction and the noise-assisted correlation algorithm (NCA) into the algorithm of Nakagami imaging to suppress the artifacts. A single-element imaging system equipped with a 5 MHz transducer was used to perform the brightness/depth (B/D) scanning of agar phantoms with scatterer concentrations ranging from 2 to 32 scatterers/mm(3). Experiments were also carried out on a mass with some strong point reflectors in a breast phantom using a commercial scanner with a 7.5 MHz linear array transducer operated at multifocus mode. The multifocus radiofrequency (RF) signals after the NCA process were used for Nakagami imaging. In the experiments on agar phantoms, an increasing scatterer concentration from 2 to 32 scatterers/mm(3) led to backscattered statistics ranging from pre-Rayleigh to Rayleigh distributions, corresponding to the increase in the Nakagami parameter measured in the focal zone from 0.1 to 0.8. However, the artifacts in the far field resulted in the Nakagami parameters of various scatterer concentrations to be close to 1 (Rayleigh distribution), making Nakagami imaging difficult to characterize scatterers. In the same scatterer concentration range, multifocus Nakagami imaging with the NCA simultaneously suppressed two types of artifacts, making the Nakagami parameter increase from 0.1 to 0.8 in the focal zone and from 0.18 to 0.7 in the far field, respectively. In the breast phantom experiments, the backscattered statistics of the mass corresponded to a high degree of pre-Rayleigh distribution. The Nakagami parameter of the mass before and after artifact reduction was 0.7 and 0.37, respectively. The results demonstrated that the proposed method for

  8. The effect of transducer characteristics on the estimation of Nakagami paramater as a function of scatterer concentration.

    PubMed

    Tsui, Po-Hsiang; Wang, Shyh-Hau

    2004-10-01

    The effect of transducer characteristics on the sensitivity of the Nakagami parameter to detect the variation of scatterer concentrations was studied. The rationale for this study stems from our pilot results which showed that the Nakagami parameters, estimated using a nonfocused transducer were not as sensitive as those of measurements using a commercial ultrasonic scanner in previous reports. This discrepancy may be attributed to the effects of transducer characteristics relative to the size of the resolution cell as verified by measurements of phantoms and 2-D computer simulations. The Nakagami parameter as a function of scatterer concentration was calculated using backscattered signals acquired from the scattering medium of different scatterer concentrations ranging from 2 to 32 scatterers/mm(3) using both 5 MHz nonfocused and focused transducers. Experimental and simulation results obtained from the nonfocused transducer represent that their respective Nakagami parameters increased from 1.17 to 1.31 and from 0.82 to 1.01 corresponding to the increase of scatterer concentrations. For the results obtained from the focused transducer, their average Nakagami parameters increased from 0.27 to 0.72 and from 0.33 to 0.81. These consistent results demonstrated that Nakagami parameter estimated using a focused transducer tends to be more sensitive than that by a nonfocused transducer to detect the variation of low scatterer concentration. This difference is fully due to the effect of transducer characteristics associated with the effective number of scatterers in the resolution cell.

  9. 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.

  10. Effects of fading and interference in narrowband land-mobile networks

    NASA Astrophysics Data System (ADS)

    Linnartz, Johan Paul Marie Gerard

    1991-05-01

    The performance of mobile radio systems with narrowband radio channels is studied. Several results of previous research are included. In particular, the effects of multipath and shadow 'fading' and of mutual 'interference' between mobile users is investigated. To this end, initially the relevant propagation mechanisms are addressed, focusing on statistical channel models. For the planning of real systems, the suitability of some propagation models using terrain data is empirically evaluated. The statistical channel description is used to compute the performance of mobile radio links. Expressions are given for the outage probability and for the average duration of fades, taking account of mutual interference between users. A simplified model for the bit error rate in digital transmission is proposed. Numerical results are given for mobile telephone networks.

  11. The Parametric Images of Microbubbles and Tissue Mimicking Phantoms Based on the Nakagami Parameters Map

    NASA Astrophysics Data System (ADS)

    Nardjess, Bahbah; Hakim, Djelouah; Bouakaz, A.

    The ultrasonic B-mode imaging is an important clinical tool used to examine internal structures of biological tissue and contrast microbubbles. To overcome the drawbacks of conventional B-scans which cannot fully reflect the nature of the tissue, other imaging methods based on stochastic models are proposed. Among these models, the Nakagami statistical model was chosen, because it is more general and simpler to apply than other statistical models (Rayleigh and K models), to generate parametric images based on the Nakagami parameters. Experiments were performed using a 2.5 MHz linear array connected to an open research platform. A commercially phantom was used to mimic tissue and microbubbles backscatters. For several regions of interest and for different microbubbles dilutions, the RF signals have been generated at 3 and 5 transmit cycles. The Nakagami image can be combined with the use of the B-mode image simultaneously to visualize the tissue and the contrast microbubbles structures for a better medical diagnosis.

  12. Nakagami-based total variation method for speckle reduction in thyroid ultrasound images.

    PubMed

    Koundal, Deepika; Gupta, Savita; Singh, Sukhwinder

    2016-02-01

    A good statistical model is necessary for the reduction in speckle noise. The Nakagami model is more general than the Rayleigh distribution for statistical modeling of speckle in ultrasound images. In this article, the Nakagami-based noise removal method is presented to enhance thyroid ultrasound images and to improve clinical diagnosis. The statistics of log-compressed image are derived from the Nakagami distribution following a maximum a posteriori estimation framework. The minimization problem is solved by optimizing an augmented Lagrange and Chambolle's projection method. The proposed method is evaluated on both artificial speckle-simulated and real ultrasound images. The experimental findings reveal the superiority of the proposed method both quantitatively and qualitatively in comparison with other speckle reduction methods reported in the literature. The proposed method yields an average signal-to-noise ratio gain of more than 2.16 dB over the non-convex regularizer-based speckle noise removal method, 3.83 dB over the Aubert-Aujol model, 1.71 dB over the Shi-Osher model and 3.21 dB over the Rudin-Lions-Osher model on speckle-simulated synthetic images. Furthermore, visual evaluation of the despeckled images shows that the proposed method suppresses speckle noise well while preserving the textures and fine details.

  13. 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.

  14. 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

  15. "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…

  16. Signal Classification in Fading Channels Using Cyclic Spectral Analysis

    DTIC Science & Technology

    2009-07-01

    efficient algorithms to detect and classify an OFDM signal based on its cyclic prefix through the use of a simple autocorrelation procedure [21–23...we focus on the case of an OFDM signal transmitted with no cyclic prefix. Therefore, an intermediate stage is needed between the SOF- based ...classifications and the HOCS- based classifications. A simple yet effective method to distinguish OFDM signals from the single carrier signals in question is

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

    PubMed

    Andrews, L C; Phillips, R L; Yu, P T

    1995-11-20

    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°. 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 µrad off the optical beam axis.

  18. The influence of lowpass filtering and the effects of fading on the group demodulation of QPSK signals

    NASA Astrophysics Data System (ADS)

    Secord, Norman; Isobe, Shunkichi; Loo, Chun

    The influence of the lowpass filter at the front end of a digital group demodulator on the number of usable satellite communication channels is discussed. A Monte Carlo simulation study was undertaken using a raised cosine filter as the lowpass filter response. The group demodulator was designed to accommodate 16 channels of quadrature phase shift keying data with a channel spacing equal to twice the symbol rate. In particular, it is shown that the proper design of this lowpass filter can provide several additional channels. The effects of fading and shadowing on the performance of a signal that is group demodulated are also discussed. The results indicate that the inter-channel interference that is present due to the close channel spacing of the signals combines with the fading to produce a severely distorted signal. This indicates that new receiver structures and the introduction of coding will be required to combat the fading, shadowing, and inter-channel interference for land mobile communications with on-board processing or group demodulation.

  19. 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.

  20. Early detection of liver fibrosis in rats using 3-D ultrasound Nakagami imaging: a feasibility evaluation.

    PubMed

    Ho, Ming-Chih; Tsui, Po-Hsiang; Lee, Yu-Hsin; Chen, Yung-Sheng; Chen, Chiung-Nien; Lin, Jen-Jen; Chang, Chien-Cheng

    2014-09-01

    We investigated the feasibility of using 3-D ultrasound Nakagami imaging to detect the early stages of liver fibrosis in rats. Fibrosis was induced in livers of rats (n = 60) by intraperitoneal injection of 0.5% dimethylnitrosamine (DMN). Group 1 was the control group, and rats in groups 2-6 received DMN injections for 1-5 weeks, respectively. Each rat was sacrificed to perform 3-D ultrasound scanning of the liver in vitro using a single-element transducer of 6.5 MHz. The 3-D raw data acquired at a sampling rate of 50 MHz were used to construct 3-D Nakagami images. The liver specimen was further used for histologic analysis with hematoxylin and eosin and Masson staining to score the degree of liver fibrosis. The results indicate that the Metavir scores of the hematoxylin and eosin-stained sections in Groups 1-4 were 0 (defined as early liver fibrosis in this study), and those in groups 5 and 6 ranged from 1 to 2 and 2 to 3, respectively. To quantify the degree of early liver fibrosis, the histologic sections with Masson stain were analyzed to calculate the number of fiber-related blue pixels. The number of blue pixels increased from (2.36 ± 0.79) × 10(4) (group 1) to (7.68 ± 2.62) × 10(4) (group 4) after DMN injections for 3 weeks, indicating that early stages of liver fibrosis were successfully induced in rats. The Nakagami parameter increased from 0.36 ± 0.02 (group 1) to 0.55 ± 0.03 (group 4), with increasing numbers of blue pixels in the Masson-stained sections (p-value < 0.05, t-test). We concluded that 3-D Nakagami imaging has potential in the early detection of liver fibrosis in rats and may serve as an image-based pathologic model to visually track fibrosis formation and growth.

  1. [On NAKAGAMI Kinkei's Seiseido Rogosetsu (a commentary on Rongo): bibliography, philology, and philosophy of medicine].

    PubMed

    Tateno, Masami

    2006-12-01

    NAKAGAMI, Kinkei's Seiseido Rogosetsu is one of his main works. It has been handed down merely as a manuscript copy. It conveys the contents regarding Kinkei's own understanding of the phrases in the Rongo, his inquiry on those sentences based on the shapes of characters, and his will for revolution. He wrote this volume because he was influenced by OGYU Sorai's commentary and he wanted to clarify his own profound medical view based on the idea that Confucianism and medicine were derived from one common origin. Accordingly, his understanding of the Rongo is above the level of a mere commentary and it has a profound philosophy of medicine.

  2. Evaluate thermal lesion using Nakagami imaging for monitoring of high-intensity focused ultrasound

    NASA Astrophysics Data System (ADS)

    Zhang, Siyuan; Li, Chong; Zhou, Fanyu; Wang, Supin; Wan, Mingxi

    2017-03-01

    High-intensity focused ultrasound (HIFU) is currently being developed as a noninvasive technique for the treatment of cancer located in various tissues. Cavitation microbubbles (MBs) have been potential to aid treatment while the acoustic posterior shadowing effects of MBs influence the accuracy for defining the location and range of ablated thermal lesions during focused ultrasound surgery when using ultrasonic monitoring imaging. This work explored the feasibility of using ultrasonic Nakagami imaging to evaluate the ablated region induced by focused ultrasound exposures at different acoustic power levels in transparent tissue-mimicking phantoms.

  3. Backwards Fading to Speed Task Learning

    DTIC Science & Technology

    2013-09-01

    Schaefer: 14. ABSTRACT (Maximum 200 words): In Backwards Fading (BF), a learner is provided with an initial, complete demonstration of a multi ...promise for effective/efficient training, but the utility of BF in Army settings and with Army tasks needs to be empirically evaluated. To that end...accelerated BF resulted in poorer performance than gradual BF (Experiment 2). Recommendations for utilizing BF in Army settings are provided. 15

  4. Comparison of hybrid FDMA/CDMA systems in frequency selective Rayleigh fading

    NASA Astrophysics Data System (ADS)

    Eng, Thomas; Milstein, Laurence B.

    1994-06-01

    A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signaling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal.

  5. Capacity fade of Sony 18650 cells cycled at elevated temperatures. Part II. Capacity fade analysis

    NASA Astrophysics Data System (ADS)

    Ramadass, P.; Haran, Bala; White, Ralph; Popov, Branko N.

    A complete capacity fade analysis was carried out for Sony 18650 cells cycled at elevated temperatures. The major causes of capacity loss were identified and a complete capacity fade balance was carried out to account for the total capacity loss of Li-ion battery as a function of cycle number and temperature. The three most significant parameters that cause capacity loss were loss of secondary active material (LiCoO 2/carbon) and primary active material (Li +) and the rate capability losses. Intrinsic capacity measurements for both positive and negative electrode has been used to estimate the capacity loss due to secondary active material and a charge balance gives the capacity lost due to primary active material (Li +). Capacity fade has been quantified with secondary active material loss dominating the other losses.

  6. Fading correlation and analytical performance evaluation of the space-diversity free-space optical communications system

    NASA Astrophysics Data System (ADS)

    Yang, G.; Khalighi, M. A.; Bourennane, S.; Ghassemlooy, Z.

    2014-03-01

    This paper investigates fading correlation in space-diversity free-space optical (FSO) communication systems and its effect on the link performance. We firstly evaluate the fading correlation in multiple-aperture FSO systems using wave-optics simulations. The influence of different system parameters including the link distance and aperture spacing is illustrated under realistic beam propagation conditions. In particular, we show that, at relatively large link distances where the scattering disk is much larger than the receiver aperture size, the fading correlation coefficient is almost independent of the apertures’ diameter and depends only on the apertures’ edge separation. To investigate the impact of fading correlation on the system’s performance, we propose an analytical approach to evaluate the performance of the space-diversity FSO system over a correlated Gamma-Gamma (ΓΓ) fading channel. Our approach is based on approximating the sum of arbitrarily correlated ΓΓ random variables by an α-μ distribution. To validate the accuracy of this method, we evaluate the average bit-error-rate (BER) performance for the case of a multiple-aperture FSO system and compare it with the BER results obtained via Monte Carlo simulations.

  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. Channel simulation for optical communication systems

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.

    1974-01-01

    A technique is reported for simulating the signal fading that will be experienced by typical optical communication systems. The desired irradiance or amplitude fading statistics can be simulated by incorporating a linearized optical modulator subsystem between the transmitter and receiver. This technique has been implemented in the design and construction of a laboratory channel simulator. The design of the processing electronics is discussed along with the results of tests performed for each mode of operation.

  10. 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.

  11. Multipath fading analysis of telemetry signals power fluctuations from Universitetsky microsatellite

    NASA Astrophysics Data System (ADS)

    Shakhparonov, Vladimir; Millán Adán, Espinoza; Vicente Vivas, Esaú

    2012-03-01

    The article deals with the results of the fading fluctuations analysis for telemetry signals in the 2 m and 70 cm bands from the first Moscow State University microsatellite better known as "Universitetsky". Radio telemetry signals were received from the microsatellite for around 2 years, collecting and recording the power signal data of almost 7500 satellite overpasses. The received signals from about 2300 satellite overpasses had a very low signal to noise ratio (SNR) that caused high transmission losses. The rest of the signals had a SNR high enough to complete the transmission without losses. The main objective of this paper was to find the fading fluctuations caused both by diffusion and by the presence of Gaussian and non Gaussian noise in telemetry signal power data. The purpose was both to characterize the communication channel as well as to elaborate solutions both to improve the communication quality as well as to identify no homogeneous zones in the ionosphere environment. The signal power analysis was based in the observation of statistical characteristics from different power signal components, in particular the components influenced by diffusion and non Gaussian noise. The employed methodology follows the next steps: removing the power signal envelope; taking away the Gaussian noise; obtaining the statistical characteristics from non Gaussian noise, Gaussian noise and envelope; finally identifying the LOS and NLOS signal fading components. For this purpose, the wavelet technique was used to perform the signal decomposition. In particular, the discrete wavelet transform DWT was utilized to carry out the signal de-noising. Then, the results were statistically treated in order to obtain a diffusion index for Rician fading, which are associated with fading in atmosphere and ionosphere layers. In this way the communications channel among satellite and ground station was characterized and a BER parameter was obtained for every satellite overpass, which

  12. Why does consciousness fade in early sleep?

    PubMed

    Tononi, Giulio; Massimini, Marcello

    2008-01-01

    Consciousness fades during deep nonrapid eye movement (NREM) sleep early in the night, yet cortical neurons remain active, keep receiving sensory inputs, and can display patterns of synchronous activity. Why then does consciousness fade? According to the integrated information theory of consciousness, what is critical for consciousness is not firing rates, sensory input, or synchronization per se, but rather the ability of a system to integrate information. If consciousness is the capacity to integrate information, then the brain should be able to generate consciousness to the extent that it has a large repertoire of available states (information), yet it cannot be decomposed into a collection of causally independent subsystems (integration). A key prediction stemming from this hypothesis is that such ability should be greatly reduced in deep NREM sleep; the dreamless brain either breaks down into causally independent modules, shrinks its repertoire of possible responses, or both. In this article, we report the results of a series of experiments in which we employed a combination of transcranial magnetic stimulation and high-density electroencephalography (TMS/hd-EEG) to directly test this prediction in humans. Altogether, TMS/hdEEG measurements suggest that the sleeping brain, despite being active and reactive, loses its ability of entering states that are both integrated and differentiated; it either breaks down in causally independent modules, responding to TMS with a short and local activation, or it bursts into an explosive and aspecific response, producing a full-fledged slow wave.

  13. 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.

  14. Fading characteristics of panchromatic radar backscatter from selected agricultural targets

    NASA Technical Reports Server (NTRS)

    Bush, T. F.; Ulaby, F. T.

    1973-01-01

    An experiment was performed to empirically determine the fading characteristics of backscattered radar signals from four agricultural targets at 9 GHz. After a short review of the statistics of Rayleigh fading backscatter, the data processing method and results of the data are analyzed. Comparison with theory shows adequate agreement with the experimental results, provided of course, the targets are modeled in a correct manner.

  15. Restoration Of Faded Color Photographs By Digital Image Processing

    NASA Astrophysics Data System (ADS)

    Gschwind, Rudolf

    1989-10-01

    Color photographs possess a poor stability towards light, chemicals heat and humidity. As a consequence, the colors of photographs deteriorate with time. Because of the complexity of processes that cause the dyes to fade, it is impossible to restore the images by chemical means. It is therefore attempted to restore faded color films by means of digital image processing.

  16. 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.

  17. Beam-tracking in FSO links impaired by correlated fading

    NASA Astrophysics Data System (ADS)

    Kiasaleh, Kamran

    2006-08-01

    In this paper, the performance of quad-APD spatial tracking loop (STL)in the presence of scintillation is studied for a frozen atmosphere turbulent model for free-space communications (FSO). The atmospheric turbulence responsible for the beam scintillation is assumed to follow the weak turbulence model, described by Rytov approximation, which in turn suggests log-normal statistics for the received optical signal intensity. It is assumed that pointing error in large part is due to atmospheric wander and that the correlation time of the beam wander is comparable to the correlation time of the amplitude variations due to amplitude scintillation. Provided recently reported estimation strategies, a new model for spatial tracking is proposed where estimates of channel coefficient are used to adjust the gain of the tracking loop, enabling an adaptive bandwidth adjustment in the presence of correlated fading. The performance of the proposed loop as well as that of the standard tracking loop are assessed and compared via simulation in terms of the mean square tracking error (MSTE).

  18. Using ultrasound backscattering signals and Nakagami statistical distribution to assess regional cataract hardness.

    PubMed

    Caixinha, Miguel; Jesus, Danilo A; Velte, Elena; Santos, Mário J; Santos, Jaime B

    2014-12-01

    This study aims to analyze the protein aggregates spatial distribution for different cataract degrees, and correlate this information with the lens acoustical parameters and by this way, assess the cataract regional hardness. Different cataract degrees were induced ex vivo in porcine lenses. A 25 MHz ultrasonic transducer was used to obtain the acoustical parameters (velocity, attenuation, and backscattering signals). B-scan and Nakagami images were constructed. Also, lenses with different cataract degrees were sliced in two regions (nucleus and cortex), for fibers and collagen detection. A significant increase with cataract formation was found for the velocity, attenuation, and brightness intensity of the B-scan images and Nakagami m parameter ( ). The acoustical parameters showed a good to moderate correlation with the m parameter for the different stages of cataract formation. A strong correlation was found between the protein aggregates in the cortex and the m parameter. Lenses without cataract are characterized using a classification and regression tree, by a mean brightness intensity ≤0.351, a variance of the B-scan brightness intensity ≤0.070, a velocity ≤1625 m/s, and an attenuation ≤0.415 dB/mm·MHz (sensitivity: 100% and specificity: 72.6%). To characterize different cataract degrees, the m parameter should be considered. Initial stages of cataract are characterized by a mean brightness intensity >0.351 and a variance of the m parameter >0.110. Advanced stages of cataract are characterized by a mean brightness intensity >0.351, a variance of the m parameter ≤0.110, and a mean m parameter >0.374. For initial and advanced stages of cataract, a sensitivity of 78.4% and a specificity of 86.5% are obtained.

  19. A PSAM-based estimator of noise and fading statistics for optimum receivers of free space optics signals

    NASA Astrophysics Data System (ADS)

    Moradi, Hassan; Refai, Hazem H.; LoPresti, Peter G.; Atiquzzaman, Mohammed

    2010-02-01

    Incoherent receivers of Free Space Optical (FSO) signals have no knowledge of instantaneous channel state. Thus, the receiver requires some information about the noise and fading statistics for a maximum likelihood (ML)-based optimal detection. Using pilot-aided symbols, we develop a simple multi slot averaging (MSA) estimation technique to approximate the values of parameters required at the incoherent detector. No channel state information (CSI) is available at the receiver side and this work will not be also trying to estimate it. But the estimation of noise and fading statistics will be practically investigated. We evaluate the bit error rate (BER) performance of FSO links with MSA estimation over both Gaussian and lognormal atmospheric turbulence fading (scintillation) channels. Numerical simulation will be completed to evaluate the estimation error of the MSA estimator. We will see that at signal to noise ratio (SNR)=13dB, the performance loss of the Gaussian estimator improves from 3dB to 0.4dB when we increase the number of pilot symbols from 16 to 64. This paper also presents the hardware design of the estimator using Xilinx system generator.

  20. Fade detector for the FODA-TDMA access scheme

    NASA Astrophysics Data System (ADS)

    Celandroni, Nedo; Ferro, Erina; Marzoli, Antonio

    1989-05-01

    The First in first out Ordered Demand Assignment-Time Division Multiple Access (FODA-TDMA) satellite access scheme designed for simultaneous transmissions of real time data, like packetized voice and slow-scan images (stream traffic) and data coming from standard EDP applications, such as bulk data tansfer, interactive computer access, mailing, data base enquiry and updating (datagram traffic) is described. When deep fades are experienced due to rain attenuation, the system is able to counter the fade. Techniques to detect the fade are presented.

  1. An examination of ham colour fading using optical fibre methods

    NASA Astrophysics Data System (ADS)

    Sheridan, Cormac; O'Farrell, Marion; Lewis, Elfed; Flanagan, Colin; Kerry, John F.; Jackman, Nick

    2006-10-01

    Sliced ham products undergo significant discolouration and fading when placed in retail display cabinets. This is due to factors such as illumination of the display cabinet, packaging, i.e. low OTR (Oxygen Transmission Rate) or very low OTR packaging, product to headspace ratio and percentage of residual oxygen. This paper presents initial investigations into the development of a sensor to measure rate of colour fading in cured ham, in order to predict an optimum colour sell-by-date. An investigation has been carried out that shows that spectral reflections offer more reproducibility than CIE L*a*b* readings, which are, at present, most often used to measure meat colour. Self-Organising Maps were then used to classify the data into five colour fading stages, from very pink to grey. The results presented here show that this classifier could prove an effective system for determining the rate of colour fading in ham.

  2. 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.

  3. 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

  4. Motion fading is driven by perceived, not actual angular velocity.

    PubMed

    Kohler, P J; Caplovitz, G P; Hsieh, P-J; Sun, J; Tse, P U

    2010-06-01

    After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. Here we examine the relationship between such 'motion fading' and perceived angular velocity. Using several different dot patterns that generate emergent virtual contours, we demonstrate that whenever there is a difference in the perceived angular velocity of two patterns of dots that are in fact rotating at the same angular velocity, there is also a difference in the time to undergo motion fading for those two patterns. Conversely, whenever two patterns show no difference in perceived angular velocity, even if in fact rotating at different angular velocities, we find no difference in the time to undergo motion fading. Thus, motion fading is driven by the perceived rather than actual angular velocity of a rotating stimulus.

  5. 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.

  6. 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.

  7. Theoretical study of a dynamic simulator of selective fading for digital, wireless beam microwave links

    NASA Astrophysics Data System (ADS)

    Bouidene, A.; Vandamme, P.

    1984-10-01

    A channel simulator for line-of-sight digital radio systems is presented. The basic principle is to reproduce channel transfer functions measured in the field during multipath propagation activity, by driving a complex linear transversal filter with precomputed data. The criterion used for calculating the values of the filter taps for each transfer function is the minimum mean square error criterion. It is shown that a thirteen-taps complex transversal filter with a period of 70 MHz in the frequency domain leads to accurate simulations of selective fading transfer functions in a 50 MHz bandwidth. Technological features are investigated. Effects of the accuracy in the delays implementation and of the tap-weight quantification are particularly analyzed.

  8. Digital data communications over microwave radio channels

    NASA Astrophysics Data System (ADS)

    Salz, J.

    1984-10-01

    A major contribution to system outage in a terrestrial digital radio channel is deep fading of the frequency transfer characteristic, which in addition to causing a precipitous drop in received signal-to-noise ratio also causes signal dispersion that can result in severe intersymbol interference. Because the temporal variation of the channel is slow compared to the signaling rate, the information theoretic channel capacity and the efficiency index in bits/cycle can be viewed as random processes. Based on an established mathematical model for fading channels, the probability distribution of channel capacity and the distribution of efficiency indices for different communications techniques are estimated. A crucial obstacle to achieving these rates is the nonlinear distortion introduced by power amplifiers. A method for coping with this nonlinear distortion is also described.

  9. 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.

  10. Flow quantification with nakagami parametric imaging for suppressing contrast microbubbles attenuation.

    PubMed

    Gu, Xiaolin; Wei, Min; Zong, Yujin; Jiang, Hujie; Wan, Mingxi

    2013-04-01

    Flow quantification with contrast-enhanced ultrasound is still limited by the effects of contrast microbubble attenuation. Nakagami parametric imaging (NPI) based on the m parameter, which is related to the statistical property of echo envelope, is implemented to suppress contrast attenuation. Flow velocity (FV) and volumetric flow rate (VFR) are estimated through the least square fitting of burst depletion kinetic model to time m parameter curves (TMCs). A non-recirculating flow phantom is imaged as contrast microbubbles are infused at 10, 15, 20, 25, and 30 mL/min. Contrast microbubbles with two different concentrations are used to generate variations of contrast microbubble attenuation. The results suggest that 4 × 4 mm(2) is the optimal size of a sliding window of NPI for flow quantification under current experiment condition. At a lower microbubble concentration, the FV calculated from TMCs correlates strongly with actual FV in both unattenuated (R(2) = 0.97; p < 0.01) and attenuated regions (R(2) = 0.92; p < 0.01) within phantom. And there is a strong correlation (R(2) = 0.98; p < 0.01; slope = 0.96; intercept = 0.68) between VFR calculated from TMCs and actual VFR within the whole phantom. Similar results are obtained at higher microbubble concentrations. Compared with conventional ultrasound imaging that is intensity dependent, NPI achieves better performance on flow quantification in the presence of contrast microbubble attenuation.

  11. 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

  12. 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.

  13. Communication Channel Estimation and Waveform Design: Time Delay Estimation on Parallel, Flat Fading Channels

    DTIC Science & Technology

    2010-02-01

    Unclassified 19b. TELEPHONE NUMBER (Include area code ) (301) 394-1239 Standard Form 298 (Rev. 8/98) Prescribed by ANSI Std. Z39.18 Contents 1...Bayesian Bounds for Matched-field Parameter Estimation. IEEE Trans. on Sig. Proc. December 2004, 52 (12), 3293 –3305. 58. Ziv, J.; Zakai, M. Some Lower

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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)

  3. 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.…

  4. 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)

  5. 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)

  6. 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,…

  7. 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.

  8. 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.

  9. Combining Stimulus Fading, Reinforcement, and Extinction To Treat Food Refusal.

    ERIC Educational Resources Information Center

    Freeman, Kurt A.; Piazza, Cathleen C.

    1998-01-01

    The food refusal of a 6-year-old girl with autism and 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. (Author/CR)

  10. Power fade and capacity fade resulting from cycle-life testing of Advanced Technology Development Program lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Wright, R. B.; Christophersen, J. P.; Motloch, C. G.; Belt, J. R.; Ho, C. D.; Battaglia, V. S.; Barnes, J. A.; Duong, T. Q.; Sutula, R. A.

    This paper presents the test results and analysis of the power and capacity fade resulting from the cycle-life testing using PNGV (now referred to as FreedomCAR) test protocols at 25 and 45 °C of 18650-size Li-ion batteries developed by the US Department of Energy sponsored Advanced Technology Development (ATD) Program. Two cell chemistries were studied, a Baseline chemistry that had a cathode composition of LiNi 0.8Co 0.15Al 0.05O 2 with binders, that was cycle-life tested at 25 and 45 °C, and a Variant C chemistry with a cathode composition of LiNi 0.8Co 0.10Al 0.10O 2 with binders, that was tested only at 45 °C. The 300 Wh power, and % power fade were determined as a function of test time, i.e. the number of test cycles for up to 44 weeks (369,600 test cycles) for the Baseline cells, and for 24 weeks (201,600 test cycles) for the Variant C cells. The C/1 and C/25 discharge capacity and capacity fade were also determined during the course of these studies. The results of this study indicate that the 300 Wh power for the Baseline cells tested at 25 °C (up to 44 weeks of testing) decreased as a linear function of test time. The % power fade for these cells increased as a linear function of test time. The Baseline cells tested at 45 °C (up to 44 weeks of testing) displayed a decrease in their power proportional to the square root of the test time, with a faster rate of decrease of the power occurring at ˜28 weeks of testing. The % power fade for these cells also increased as the square root of the test time, and exhibited an increase in the % power fade rate at ˜28 weeks of testing. The 45 °C tested Baseline cells' power decreased, and their % power fade increased at a greater rate than the 25 °C tested Baseline cells. The power fade was greater for the Variant C cells. The power of the Variant C cells (tested at 45 °C) decreased as the square root of the test time, and their % power fade was also found to be a function of the square root of the test time

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    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.

  13. Channel Estimation in DCT-Based OFDM

    PubMed Central

    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. PMID:24757439

  14. An Approach to the Development of Software for Computer-Aided Design of Satellite Communications Receivers for Operation in Scintillating Channels

    DTIC Science & Technology

    1989-04-28

    coherent BPSK and for coherent offset quaternary PSK ( OQPSK ). The different curves in these figures show the effect of different channel decorrelation...77=-- --- - - 7 ~ To/Tcb - TO/Tcb =10 05101202303 1012 7 _ 7---7 7-77 COHERENT OQPSK -BLTcb)= V30 RAYLEIGH FADING f-4 FADING SpECTRUM - roTcb =30

  15. Effectiveness of Convolutional Code in Multipath Underwater Acoustic Channel

    NASA Astrophysics Data System (ADS)

    Park, Jihyun; Seo, Chulwon; Park, Kyu-Chil; Yoon, Jong Rak

    2013-07-01

    The forward error correction (FEC) is achieved by increasing redundancy of information. Convolutional coding with Viterbi decoding is a typical FEC technique in channel corrupted by additive white gaussian noise. But the FEC effectiveness of convolutional code is questioned in multipath frequency selective fading channel. In this paper, how convolutional code works in multipath channel in underwater, is examined. Bit error rates (BER) with and without 1/2 convolutional code are analyzed based on channel bandwidth which is frequency selectivity parameter. It is found that convolution code performance is well matched in non selective channel and also effective in selective channel.

  16. Spoon distance fading with and without escape extinction as treatment for food refusal.

    PubMed

    Rivas, Kristi D; Piazza, Cathleen C; Patel, Meeta R; Bachmeyer, Melanie H

    2010-01-01

    Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and without escape extinction (EE), and compared fading plus EE to EE alone. Initially, inappropriate mealtime behavior decreased during fading, but this effect was not maintained as fading progressed. Inappropriate mealtime behavior was lower initially when we combined fading and EE relative to EE alone, but acceptance increased more rapidly with EE than with fading plus EE. These results suggest that a number of mealtime characteristics might function as MOs for escape behavior and that analyses of MOs may be useful for developing treatments for food refusal.

  17. Use of texture fading in the treatment of food selectivity.

    PubMed

    Shore, B A; Babbitt, R L; Williams, K E; Coe, D A; Snyder, A

    1998-01-01

    Children with feeding disorders often display severe food selectivity. For many of these children, consuming highly textured foods may be aversive or potentially dangerous because of frequent gagging. The purpose of this study was to demonstrate the efficacy of texture fading in the treatment of food selectivity displayed by 4 children. Treatment involved the gradual addition of higher textures based on the results of periodic probes. In addition, food acceptance and swallowing were reinforced, while food refusal and food expulsion were placed on extinction. Results showed that all participants successfully advanced to consumption of age-appropriate texture and volume. The results suggest that texture fading with intermittent probes at higher textures may be an effective method for the treatment of food selectivity by texture.

  18. 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.

  19. Retention and Fading of Military Skills: Literature Review

    DTIC Science & Technology

    2000-04-01

    survey of the scientific and technical literature on models of skill fading and tools for determining when refresher training is required. In particular...the literature review investigated models for predicting skill retention relevant to the military domain. Skill retention can be defined as the...performance environments. • Type of task • Method of testing. • Individual differences. The literature review then examines several classes of models for

  20. 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.

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Prediction of fading phenomena in land-satellite communication links

    NASA Astrophysics Data System (ADS)

    Blaunstein, N.; Cohen, Y.; Hayakawa, M.

    2010-12-01

    This paper addresses the problem of prediction of probability of successful radio communication of any mobile or stationary subscriber located in areas of service such as complex urban environments characterized by nonline-of-sight propagation conditions, which limit GPS, Low Earth Orbit, and Medium Earth Orbit services in land-satellite communications. It presents a self-consistent physical-statistical approach for predicting fading phenomena usually occurring in land-satellite communication links caused by influence of the terrain features on radio signal propagation from the ground-based to the satellite antenna. This approach combines (1) the statistical description of the buildings array located on the rough terrain and the buildings' overlay profile, based on special probabilistic distributions of built-up terrain parameters, and (2) the theoretical description of propagation phenomena, taking into account multiple scattering, reflection, and diffraction mechanisms. A new technique is proposed for predicting the probability of fading phenomena occurring in land-satellite links using the so-called stochastic multiparametric model. Results of theoretical predictions are compared with those obtained from the "pure statistical" Lutz model and physical-statistical Saunders-Evans model, and then with experimental data obtained for different European cities. Obtained results show that the proposed stochastic approach can be used as a good predictor of fading phenomena in land-satellite communication links for different satellite constellation scenarios and elevations of satellites during their movement surrounding the Earth, with respect to the ground-based antenna for different land environments: rural, mixed residential, suburban, and urban.

  7. Modeling capacity fade in lithium-ion cells.

    SciTech Connect

    Liaw, Bor Yann; Doughty, Daniel Harvey; Nagasubramanian, Ganesan; Jungst, Rudolph George

    2003-09-01

    Battery life is an important, yet technically challenging, issue for battery development and application. Adequately estimating battery life requires a significant amount of testing and modeling effort to validate the results. Integrated battery testing and modeling is quite feasible today to simulate battery performance, and therefore applicable to predict its life. A relatively simple equivalent-circuit model (ECM) is used in this work to show that such an integrated approach can actually lead to a high-fidelity simulation of a lithium-ion cell's performance and life. The methodology to model the cell's capacity fade during thermal aging is described to illustrate its applicability to battery calendar life prediction.

  8. Fade duration statistics for Ku-band satellite links

    NASA Astrophysics Data System (ADS)

    Mandeep, J. S.

    2013-08-01

    Fade duration database was built to enhance the study of propagation characterises in the Equatorial region. The data was measured via a beacon receiver Ku-band whereby the antenna was directed to a SUPERBIRD-C2 satellite at 12.255 GHz. The performance of the measured data has been compared with ITU-R model, Kormanyos et al. and Paulson-Gibbins. The results show that the Paulson-Gibbins fits well with measured data with a low RMS error of 0.2 dB. The number of statistics available for the equatorial is small and the periods of measurement are short compared to those for temperate regions.

  9. 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.

  10. Fading AGN Candidates: AGN Histories and Outflow Signatures

    NASA Astrophysics Data System (ADS)

    Keel, William C.; Lintott, Chris J.; Maksym, W. Peter; Bennert, Vardha N.; Chojnowski, S. Drew; Moiseev, Alexei; Smirnova, Aleksandrina; Schawinski, Kevin; Sartori, Lia F.; Urry, C. Megan; Pancoast, Anna; Schirmer, Mischa; Scott, Bryan; Showley, Charles; Flatland, Kelsi

    2017-02-01

    We consider the energy budgets and radiative history of eight fading active galactic nuclei (AGNs), identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on timescales of ≈50,000 yr. We explore the use of minimum ionizing luminosity Qion derived from photoionization balance in the brightest pixels in Hα at each projected radius. Tests using presumably constant Palomar–Green QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGNs, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Qion values is roughly constant for a given object and therefore does not prevent such derivation. The AGNs in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈2 × 104 yr before the direct view of the nucleus. The e-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 yr. In the limit of largely obscured AGNs, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from far-infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGNs, to simulations of AGN accretion; the strongest variations over these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission

  11. 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…

  12. Using Script Fading to Promote Natural Environment Stimulus Control of Verbal Interactions among Youths with Autism

    ERIC Educational Resources Information Center

    Brown, John L.; Krantz, Patricia J.; McClannahan, Lynn E.; Poulson, Claire L.

    2008-01-01

    Script fading was used to teach three youths with autism to initiate and sustain verbal interactions under stimulus control consistent with the natural environment. The youths learned to engage in verbal interactions during simulated shopping trips and during visits to community stores. The effectiveness of script fading was examined using a…

  13. Beam evolutions of solitons in strongly nonlocal media with fading optical lattices

    NASA Astrophysics Data System (ADS)

    Dai, Zhi-Ping; Lu, Shi-Zhuan; You, Kai-Ming

    2013-01-01

    We address the impact of imprinted fading optical lattices on the beam evolution of solitons in strongly nonlocal nonlinear media. The results show that the width of the soliton experiences a change with the increasing propagation distance, the critical power for the soliton varies with the lattice fading away, and the soliton breathing is affected by the initial lattice depth and the nonlocality degree.

  14. Examining the Impact of Adaptively Faded Worked Examples on Student Learning Outcomes

    ERIC Educational Resources Information Center

    Flores, Raymond; Inan, Fethi

    2014-01-01

    The purpose of this study was to explore effective ways to design guided practices within a web-based mathematics problem solving tutorial. Specifically, this study examined student learning outcome differences between two support designs (e.g. adaptively faded and fixed). In the adaptively faded design, students were presented with problems in…

  15. 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…

  16. Spoon Distance Fading with and without Escape Extinction as Treatment for Food Refusal

    ERIC Educational Resources Information Center

    Rivas, Kristi D.; Piazza, Cathleen C.; Patel, Meeta R.; Bachmeyer, Melanie H.

    2010-01-01

    Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and…

  17. 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…

  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. Grouping Inhibits Motion Fading by Giving Rise to Virtual Trackable Features

    ERIC Educational Resources Information Center

    Hsieh, P. -J.; Tse, P. U.

    2007-01-01

    After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. The authors show that grouping can slow down the process of "motion fading," suggesting that cortical configural form analysis interacts with the computation of motion signals during motion fading. The…

  20. 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…

  1. Ultrasonic simulation of MSBLS multipath fading for orbiter landing configuration

    NASA Technical Reports Server (NTRS)

    Hayre, H. S.

    1978-01-01

    The on-shuttle antenna pattern of the MSBLS receiver, and the azimuth and elevation beamwidths were simulated by their corresponding ultrasonic transducer beams. The scanning rate for the azimuth and elevation beams was 1.75 degrees/second. The results were adjusted for full-scale maximum sinusoidal scan rates of 691 and 377 deg/sec for AZ and EL respectively. The rain drops were simulated by air bubbles, with a similar size distribution, in water. The rain volume was created along a part of the propagation path, and not on the runway, because it was found difficult to avoid an accumulation of bubbles on the runway surface and surroundings simulated by the model surface. Multipath fading from the ground, and its possible degrading effect on the orbiter received beam shape and the associated landing guidance parameters is discussed.

  2. 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.

  3. 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.

  4. The Multipath and Fading Profile of the High Latitude Meteor Burst Communication Channel.

    DTIC Science & Technology

    1986-10-01

    APPROVED: j~ ~ e. c ALLAN C. SCHELL Chief, Electromagnetic Sciences Division FOR THE COMMANDER: [ JOHN A. RITZ - Plans and Programs Division *, If your...multipath measurement VHF propagation / 19 ABSTRACT (Continue on reverse ,f necessary and identify by block number) ------ ------ .. tion High...latitude propagation phenomenon such as scatter from the aurora and sporadic-E propagation can alter the communication characteristics of the high latitude

  5. Demodulation of OFDM Signals in the Presence of Deep Fading Channels and Signal Clipping

    DTIC Science & Technology

    2012-06-01

    Power Ratio QAM Quadrature Amplitude Modulation QPSK Quadrature Phase-Shift-Keying RF Radio Frequency RMS Root Mean Square SER Symbol Error...transmitted symbols (in general a quadrature phase-shift keyed (QPSK) or a quadrature amplitude modulation (M- QAM ) signal) with observations made by...53 C. NECESSITY FOR DATA RECOVERY IN MARITIME OPERATIONAL APPLICATIONS

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Atmospheric turbulence-induced signal fades on optical heterodyne communication links

    NASA Astrophysics Data System (ADS)

    Winick, K. A.

    1986-06-01

    The three basic atmospheric propagation effects, absorption, scattering, and turbulence, are reviewed. A simulation approach is then developed to determine signal fade probability distributions on heterodyne-detected satellite links which operate through naturally occurring atmospheric turbulence. The calculations are performed on both angle-tracked and nonangle-tracked downlinks, and on uplinks, with and without adaptive optics. Turbulence-induced degradations in communication performance are determined using signal fade probability distributions, and it is shown that the average signal fade can be a poor measure of the performance degradation.

  11. Capacity and power fading mechanism identification from a commercial cell evaluation

    NASA Astrophysics Data System (ADS)

    Dubarry, Matthieu; Svoboda, Vojtech; Hwu, Ruey; Liaw, Bor Yann

    An 18650 lithium ion cell was evaluated using dynamic stress test (DST) protocol for cycle life study. Reference performance tests were applied every 60 DST cycles to quantify capacity fade and peak power capability (PPC) degradation with cycles to the end of life. A quantitative incremental capacity analysis (ICA) was applied to identify extrinsic and intrinsic contributions to capacity fading, whereas the open circuit voltage (OCV) measurements were utilized to determine the correct state of charge (SOC) in order to accurately correlate the capacity fade with SOC. The analysis also helps us identify that cell polarization resistance change in the cycles is the primary culprit that bifurcates to both extrinsic and intrinsic origins in capacity fade and PPC degradation. This analysis allows us to develop better understanding in predicting battery performance and life in the rechargeable lithium batteries.

  12. 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.

  13. 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.

  14. 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

  15. 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…

  16. Fade Analysis of ORCA DATA Beam at NTTR and Pax River

    DTIC Science & Technology

    2010-08-01

    and compare these results with UCF theoretical models. The data includes mean power in the bucket ( PIB ) and mean PIF, with and without the AO...statistical prediction model for estimating various parameters associated with the data beam, such as Fried’s parameter, Strehl ratio, PIB and PIF. In this...captured power in the bucket ( PIB ) by the receiver aperture and the fade statistics associated with the data beam. The fractional fade time (also called the

  17. MIMO FSO communication using subcarrier intensity modulation over double generalized gamma fading

    NASA Astrophysics Data System (ADS)

    Yi, Xiang; Yao, Mingwu; Wang, Xiaoyang

    2017-01-01

    Atmospheric turbulence-induced fading is known to have a serious detrimental effect on the performance of free-space optical (FSO) communication. The involvement of multiple lasers and photodetectors in FSO systems offers an effective way to overcome fading. Very recently, a new generic fading model, called double-generalized gamma (double GG), is developed for accurately describing irradiance fading over a wide range of turbulence conditions. Therefore, for a general and exact study of the multiple-input multiple-output (MIMO) FSO system, the double GG fading model is adopted in this paper. We investigate the MIMO FSO systems using subcarrier intensity modulation. Two typical transmit diversity schemes, repetition code (RC) and orthogonal space-time block code (OSTBC), are considered. We first propose a new power series expression for the probability density function of the double GG fading. Then we derive the average error rate expressions for both schemes in terms of double power series. The truncated forms of the derived power series enable the rapid and accurate numerical computation of the error rates. Furthermore, we present the asymptotic error rate analyses at high electrical signal-to-noise ratio (SNR) for both schemes. Closed-form diversity order and coding gain for both schemes are also obtained. Our numerical results, verified by simulation, confirm that RC outperforms OSTBC for MIMO FSO systems with subcarrier intensity modulation in double GG fading. The asymptotic coding gain of the RC scheme over the OSTBC scheme is analytically quantified for varying degrees of the fading strength.

  18. Neutron Fading Characteristics of Copper Doped Lithium Fluoride (LiF: MCP) Thermoluminescent Dosimeters (TLDs)

    DTIC Science & Technology

    2008-05-21

    Fading Characteristics of Copper-Doped Lithium Fluoride (LiF: MCP) Thermoluminescent Dosimeters (TLDs)" Name of Candidate: L T Jeffrey A. Delzer Master...Lithium Fluoride Thermoluminescent Dosimeters beyond brief excerpts is with the permission of the copyright owner, and will save and hold harmless...Thesis: Author: Thesis directed by: ABSTRACT "Neutron Fading Characteristics of Copper-Doped Lithium Fluoride (LiF: MCP) Thermoluminescent

  19. 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.

  20. Impact of a Backwards Faded Scaffolding Approach to Learning Astronomy

    NASA Astrophysics Data System (ADS)

    Slater, Stephanie

    2010-01-01

    The Boyer Commission Report, "Reinventing Undergraduate Education" eloquently argues that all undergraduate coursework would benefit greatly by being framed as authentic research experiences where students create and defend knowledge. Yet, our experience in guiding students to do research projects using astronomical databases has demonstrated time and time again that the most difficult aspect of engaging in scientific research is helping students identify and frame a fruitful research question itself. To scaffold students' learning experiences to help them ask better research questions, we have adopted a backwards faded scaffolding approach where students do multiple inquiry experiences, rather than a single protracted one. In this approach, we first carefully guide students through an entire astronomical inquiry sequence, from giving them the targeted research question through an accurate scientific conclusion tightly matched to the research question. Then, for their second inquiry experience, students generate their conclusions independently, with the previous experience set out as a guide. Students are required to make sense of data that has been purposefully planned, collected, and analyzed with instructor guidance. They construct and defend conclusions based upon data that is, effectively, given to them. By the time students reach their third inquiry they have been exposed to two experiences in which they were guided through the. During this third inquiry data collection and analysis becomes an independent task. By the fourth inquiry, students have received explicit instruction on the connection between the research questions and the procedure undertaken to address them three times. They are prepared to take responsibility for creating a plausible method for collecting data given a research prompt. By the fifth inquiry, students have now seen four examples of quality research questions/hypotheses, and their relationship to procedures, data collection and

  1. Channel Equalization for Single Carrier MIMO Underwater Acoustic Communications

    DTIC Science & Technology

    2010-01-01

    m(k, l) and ˜φn,m(k) are the lth complex fading coefficient and the phase drift of the time-varying subchannel between the nth transducer and the mth...for the two-transducer eight- hydrophone MIMO transmissions with BPSK and QPSK modulations, respectively. Obviously, all subchannels are sparse with two...transducer), its related channel energy is defined as the summation of all related subchannel energies. Then a simple ordering criterion is to compare the

  2. Evaluation of FEC for the atmospheric optical IM/DD channel

    NASA Astrophysics Data System (ADS)

    Henniger, Hennes; David, Florian; Giggenbach, Dirk; Rapp, Christoph

    2003-07-01

    Channel measurements were performed by the German Aerospace Center in various near ground optical channels including a 1.5 km horizontal path as well as a 61km path. These measurements clearly showed that the atmosphere causes very slow fading (compared to the high data rates usually used in optical communication systems), which significantly degrades the transmission quality. As transmitter power and receiver sensitivity are limited by the transmission technology, fading depicts a severe problem, that can be reduced by the use of forward error correction schemes (FEC) in order to improve system performance. Therefore FEC was subject of investigations by means of simulations. To figure out which FEC methods are useful for applications in the atmospheric optical channels simulations of standard block codes and interleavers have been done. They were based on data sets taken in the various channel measurements. The simulations point out that only very long interleaving can increase performance significantly.

  3. A Novel 2-D OFDM-DS-CDMA Receiver with Frequency-Time Spreading

    NASA Astrophysics Data System (ADS)

    Chen, Joy Iong-Zong

    This paper presents a novel 2-D (2-dimension) receiver that adopts the reception scheme to promote OFDM-DS-CDMA (orthogonal frequency division multiplexing multi-carrier coded-division multiple-access) system performance. The system model includes spread coding and a system block diagram of the 2-D receiver shown graphically with 3-D (three dimensions) plots. The analytical calculation of system performance for an OFDM-DS-CDMA system combined with the proposed receiver equipment is investigated. To evaluate the results from the channel fading effect is considered over the correlated fading environments. The correlated-Nakagami-m statistical distribution is taken into account in the evaluation. The results show that the number of users, the number of subcarriers and the fading channel correlation generally affect OFDM-DS-CDMA systems. The system is also influenced by the Doppler shift and the signal propagation environment (fading parameter).

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

    DOE PAGES

    Hu, E.; Lyu, Y.; Xin, H.; ...

    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

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

    SciTech Connect

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

    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 compound 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.

  6. Relationship between DAPI-fluorescence fading and nuclear DNA content: An alternative method to DNA quantification?

    PubMed

    Gallardo-Escárate, Cristian; Alvarez-Borrego, Josué; Von Brand, Elisabeth; Dupré, Enrique; Del Río-Portilla, Miguel Angel

    2007-01-01

    In observations by confocal or conventional fluorescence microscopy, important factors should be considered in order to obtain accurate images. One of them, such as the fluorescence bleaching from highest intensity to lowest signal of fluorescence is a common problem with several DNA fluorochromes and especially for DAPI stain. The fluorescence of DAPI fades rapidly when it is exposed to UV light, under optimal conditions of observation. Although the fading process can be retarded using a mounting medium with antifading reagents, the photochemical process underlying the fluorescence decay has not yet been fully explained. In addition, no relationship between fluorescence fading and nuclear DNA content has been tested. In order to test this relationship, we measured by means of image analysis the DAPI-fluorescence intensity in several cellular types (spermatozoa, erythrocytes and haemocytes) during their fluorescence bleaching. An algorithm specifically built in MATLAB software was used for this approach. The correlation coefficient between nuclear DNA content and DAPI-fluorescence fading was found equal to 99%. This study demonstrates the feasibility to measure nuclear DNA content by fluorescence fading quantification, as an alternative method concurrently with image analysis procedures.

  7. Bayesian and Frequentist Estimation of the Average Capacity of Log Normal Wireless Optical Channels

    NASA Astrophysics Data System (ADS)

    Katsis, A.; Nistazakis, H. E.; Tombras, G. S.

    2008-11-01

    We investigate the average (ergodic) capacity of practical free-space optical communication channels using the frequentist and the Bayesian approach. We concentrate on the cases of weak and moderate atmospheric turbulence leading to channels modeled by Log-Normal distributed intensity fading and derive closed-form expressions and estimation procedures for their achievable capacity and the important parameters of interest. Each methodology is reviewed in terms of their analytic convenience and their accuracy is also discussed.

  8. Pilot-Assisted Channel Estimation for Orthogonal Multi-Carrier DS-CDMA with Frequency-Domain Equalization

    NASA Astrophysics Data System (ADS)

    Shima, Tomoyuki; Tomeba, Hiromichi; Adachi, Fumiyuki

    Orthogonal multi-carrier direct sequence code division multiple access (orthogonal MC DS-CDMA) is a combination of time-domain spreading and orthogonal frequency division multiplexing (OFDM). In orthogonal MC DS-CDMA, the frequency diversity gain can be obtained by applying frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion to a block of OFDM symbols and can improve the bit error rate (BER) performance in a severe frequency-selective fading channel. FDE requires an accurate estimate of the channel gain. The channel gain can be estimated by removing the pilot modulation in the frequency domain. In this paper, we propose a pilot-assisted channel estimation suitable for orthogonal MC DS-CDMA with FDE and evaluate, by computer simulation, the BER performance in a frequency-selective Rayleigh fading channel.

  9. 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.

  10. 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

  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. Study of ageing and fading in CR-39 detectors for different storage conditions.

    PubMed

    Franci, Daniele; Aureli, Tommaso; Cardellini, Francesco

    2015-12-01

    The aim of this study was to investigate the effect of ageing and fading on PADC detector response, as a function of the storage time and temperature. Several groups of CR-39 detectors provided by Radosys, Ltd. were exposed at the reference radon chamber of the Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, at the ENEA centre in Casaccia. The results indicate that low-temperature storage inhibits the effect of both ageing and fading. Finally, the overall reduction in CR-39 sensitivity due to the combined ageing/fading effect was estimated. In particular, the sensitivity of the detectors continuously exposed in air at room temperature over 6 and 3 months was reduced, respectively, by 7.5 and 4 %.

  13. 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

  14. Investigation of signal fading in lithium formate EPR dosimeters using a new sensitive method

    NASA Astrophysics Data System (ADS)

    Adolfsson, Emelie; Karlsson, Mattias; Alm Carlsson, Gudrun; Carlsson Tedgren, Åsa; Lund, Eva; Olsson, Sara; Gustafsson, Håkan

    2012-04-01

    The aim of this study was to investigate signal fading in lithium formate electron paramagnetic resonance (EPR) dosimeters used for clinical applications in radiotherapy. A new experimental method for determination of signal fading, designed to resolve small changes in signal from slowly decaying unstable radicals, was used. Possible signal fading in lithium formate due to different storage temperatures was also tested. Air humidity was kept at a constant level of 33% throughout the experiments. The conclusion drawn from the investigations was that the EPR signal from lithium formate is stable during at least 1 month after irradiation and is not sensitive to variations in storage temperature <40 °C when kept at a relative air humidity of 33%. This makes lithium formate a suitable dosimeter for transfer dosimetry in clinical audits.

  15. Adaptive control of satellite EIRP to reduce outage caused by fading

    NASA Astrophysics Data System (ADS)

    Bakken, P. M.; Maseng, T.

    1983-05-01

    The effectiveness of dynamic satellite EIRP allocation in reducing the effects of up and downlink fading is assessed. Analytical methods using numerical convolution performed by fast Fourier transforms are used to evaluate the performance of allocation techniques in terms of the probability distribution of the satellite link quality obtained from the link fading statistics at the terminal sites. The results are presented in the form of outage statistics for particular systems and allocation methods. They represent the entire range of performance which can be envisaged, ranging from CTP to ASEIRP.

  16. 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

  17. TRP Channels

    PubMed Central

    Venkatachalam, Kartik; Montell, Craig

    2011-01-01

    The TRP (Transient Receptor Potential) superfamily of cation channels is remarkable in that it displays greater diversity in activation mechanisms and selectivities than any other group of ion channels. The domain organizations of some TRP proteins are also unusual, as they consist of linked channel and enzyme domains. A unifying theme in this group is that TRP proteins play critical roles in sensory physiology, which include contributions to vision, taste, olfaction, hearing, touch, and thermo- and osmosensation. In addition, TRP channels enable individual cells to sense changes in their local environment. Many TRP channels are activated by a variety of different stimuli and function as signal integrators. The TRP superfamily is divided into seven subfamilies: the five group 1 TRPs (TRPC, TRPV, TRPM, TRPN, and TRPA) and two group 2 subfamilies (TRPP and TRPML). TRP channels are important for human health as mutations in at least four TRP channels underlie disease. PMID:17579562

  18. "Paintings Fade Like Flowers": Pigment Analysis and Digital Reconstruction of a Faded Pink Lake Pigment in Vincent van Gogh's Undergrowth with Two Figures.

    PubMed

    Fieberg, Jeffrey E; Knutås, Per; Hostettler, Kurt; Smith, Gregory D

    2017-01-01

    Color fading in Vincent van Gogh's Undergrowth with Two Figures was studied chemically to facilitate the creation of a digital reconstruction of fugitive colors . The painting contains a field of white, green, orange, and yellow flowers under a canopy of poplar trees with two central figures-a man and a woman, arms entwined. From Van Gogh's letters, however, it is known that he painted the picture with some pink flowers, which appear to have altered, presumably to white. Raman spectroscopy was applied to microsamples of paint to identify the faded pigment as geranium lake, which in this painting consists of the dye, eosin (2',4',5',7'-tetrabromofluorescein). For the first time, lead(II) sulfate has been specifically identified as the likely inorganic substrate for a geranium lake used by Van Gogh in the last months of his life. Microfocus X-ray fluorescence (MXRF) spectroscopy was subsequently used in situ to analyze the white flowers to identify bromine as a proxy for eosin, thus indicating an original pink coloration. Of the 387 white flowers analyzed, 37.7% contained measurable bromine and were, therefore, originally pink. Several cross-sections from these formerly pink areas were assessed using a combination of visual inspection and microcolorimetry to create a colored mask in Adobe Photoshop to digitally reconstruct a suggestion of the original appearance of the painting with regard to the faded flowers. Additionally, microfadeometry was undertaken for the first time on a painting cross-section sample to understand the actual fading kinetics of the underlying bright pink geranium lake used by Van Gogh. A combination of Raman microspectroscopy, MXRF, and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) were utilized in situ and on paint microsamples to identify the complete palette used to create Undergrowth with Two Figures.

  19. 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

  20. Adaptive detection technique for optical wireless communication over strong turbulence channels

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Huang, Dexiu; Xiuhua, Yuan

    2007-11-01

    Optical wireless communication (OWC) systems use the atmosphere as a propagation medium, so the atmospheric turbulence effects lead to fading related with signal intensity. The received signal of OWC over strong turbulence channels is assumed to be a mixture of K-distributed fading and Gaussian distributed thermal noise. Second-order spectral analysis is unable to separately estimate the mixed signal. In order to mitigate the fading induced by turbulence, the decision threshold-updating algorithm based on second and higher order cumulants is proposed and is able to operate in an unknown turbulence environment. The performance of the adaptive processing scheme has been evaluated by means of Monte Carlo simulations. Simulation results show the improvement of the bit error rate (BER) performance.

  1. 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…

  2. Channel capacity of next generation large scale MIMO systems

    NASA Astrophysics Data System (ADS)

    Alshammari, A.; Albdran, S.; Matin, M.

    2016-09-01

    Information rate that can be transferred over a given bandwidth is limited by the information theory. Capacity depends on many factors such as the signal to noise ratio (SNR), channel state information (CSI) and the spatial correlation in the propagation environment. It is very important to increase spectral efficiency in order to meet the growing demand for wireless services. Thus, Multiple input multiple output (MIMO) technology has been developed and applied in most of the wireless standards and it has been very successful in increasing capacity and reliability. As the demand is still increasing, attention now is shifting towards large scale multiple input multiple output (MIMO) which has a potential of bringing orders of magnitude of improvement in spectral and energy efficiency. It has been shown that users channels decorrelate after increasing the number of antennas. As a result, inter-user interference can be avoided since energy can be focused on precise directions. This paper investigates the limits of channel capacity for large scale MIMO. We study the relation between spectral efficiency and the number of antenna N. We use time division duplex (TDD) system in order to obtain CSI using training sequence in the uplink. The same CSI is used for the downlink because the channel is reciprocal. Spectral efficiency is measured for channel model that account for small scale fading while ignoring the effect of large scale fading. It is shown the spectral efficiency can be improved significantly when compared to single antenna systems in ideal circumstances.

  3. The Effects of Spatial Diversity and Imperfect Channel Estimation on Wideband MC-DS-CDMA and MC-CDMA

    DTIC Science & Technology

    2009-10-01

    input multiple-output (MIMO) system which employs Alamouti spacetime block coding at each sub-carrier frequency to achieve spatial diversity. We...number of pilot symbols per channel estimate. 13 N/A MC-DS-CDMA, MC-CDMA, Alamouti spacetime block coding, frequency-selective Rayleigh fading

  4. 2-Step Maximum Likelihood Channel Estimation for Multicode DS-CDMA with Frequency-Domain Equalization

    NASA Astrophysics Data System (ADS)

    Kojima, Yohei; Takeda, Kazuaki; Adachi, Fumiyuki

    Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide better downlink bit error rate (BER) performance of direct sequence code division multiple access (DS-CDMA) than the conventional rake combining in a frequency-selective fading channel. FDE requires accurate channel estimation. In this paper, we propose a new 2-step maximum likelihood channel estimation (MLCE) for DS-CDMA with FDE in a very slow frequency-selective fading environment. The 1st step uses the conventional pilot-assisted MMSE-CE and the 2nd step carries out the MLCE using decision feedback from the 1st step. The BER performance improvement achieved by 2-step MLCE over pilot assisted MMSE-CE is confirmed by computer simulation.

  5. Physical Theory of Voltage Fade in Lithium- and Manganese-Rich Transition Metal Oxides

    SciTech Connect

    Rinaldo, Steven G.; Gallagher, Kevin G.; Long, Brandon R.; Croy, Jason R.; Bettge, Martin; Abraham, Daniel P.; Bareno, Javier; Dees, Dennis W.

    2015-03-04

    Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). Here, we propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due to the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈ 20% of the initial total capacity.

  6. Capacity fade study of lithium-ion batteries cycled at high discharge rates

    NASA Astrophysics Data System (ADS)

    Ning, Gang; Haran, Bala; Popov, Branko N.

    Capacity fade of Sony US 18650 Li-ion batteries cycled using different discharge rates was studied at ambient temperature. The capacity losses were estimated after 300 cycles at 2 C and 3 C discharge rates and were found to be 13.2 and 16.9% of the initial capacity, respectively. At 1 C discharge rate the capacity lost was only 9.5%. The cell cycled at high discharge rate (3 C) showed the largest internal resistance increase of 27.7% relative to the resistance of the fresh cells. The rate capability losses were proportional with the increase of discharge rates. Half-cell study and material and charge balances were used to quantify the capacity fade due to the losses of primary active material (Li +), the secondary active material (LiCoO 2/C)) and rate capability losses. It was found that carbon with 10.6% capacity loss after 300 cycles dominates the capacity fade of the whole cell at high discharge rates (3 C). A mechanism is proposed which explains the capacity fade at high discharge rates.

  7. Chebyshev-based technique for automated restoration of digital copies of faded photographic prints

    NASA Astrophysics Data System (ADS)

    Uchaev, Dmitry V.; Uchaev, Denis V.; Malinnikov, Vasiliy A.

    2017-01-01

    We present a technique for automated restoration of digital images obtained from faded photographic prints. The proposed defading technique uses our early proposed image contrast enhancement algorithm based on a contrast measure of images in the Chebyshev moment transform domain. Obtained experimental results demonstrate some advantages of the technique as compared to other widely used image enhancement methods.

  8. Physical Theory of Voltage Fade in Lithium- and Manganese-Rich Transition Metal Oxides

    DOE PAGES

    Rinaldo, Steven G.; Gallagher, Kevin G.; Long, Brandon R.; ...

    2015-03-04

    Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). Here, we propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due tomore » the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈ 20% of the initial total capacity.« less

  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. 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…

  11. HF radio signal fading and atmospheric radio noise measurements at low latitudes

    NASA Astrophysics Data System (ADS)

    Rao, S. Vijaya Bhaskara; Rao, T. Rama; Reddy, V. Gunasekhara; Lakshmi, D. R.; Veenadhari, B.; Dabas, R. S.; Ahmed, Iqbal; Gupta, M. M.; Reddy, B. M.

    2002-10-01

    Two HF broadcast transmissions, one originating from Sri Lanka (7.1°N, 79.9°E) at 11.800 MHz around the geomagnetic equator and the other from BBC, Masirah (20.6°N, 58.9°E), at 15.310 MHz several degrees north of the geomagnetic equator were monitored at Tirupati (13.5°N, 79.5°E) in southern India to compare the fading characteristics of the links. It is found that the link over the geomagnetic equator exhibits much higher fade rates as compared to the other link. The fade ranges also are, in general, higher for Sri Lanka. Fade allowances derived from these data do indicate that margins higher than those recommended by the International Telecommunication Union Radiocommunication Sector (ITU-R) need to be provided at these latitudes. The diurnal variation in the atmospheric radio noise (ARN), which sets a lower limit to the satisfactory reception of signal, over the Indian subcontinent is in total disagreement with the variations obtained at higher latitudes. This rather puzzling phenomenon has been interpreted as being due to path attenuation differentials between the LOS mode and the ionospheric mode from the lightning source because of significantly greater cloud height in the Indian region.

  12. Differences in the dynamic properties of rain fade between temperate and tropical regions

    NASA Astrophysics Data System (ADS)

    Chodkaveekityada, Peeramed; Fukuchi, Hajime

    2017-03-01

    Understanding the dynamic properties of rain attenuation is important for designing effective attenuation mitigation methods, especially for Ka-band frequencies, which are particularly sensitive to degradation by rain attenuation. In this paper, the fade duration and fade slope are estimated using satellite data from Thailand and Japan, to investigate the characteristics of rain attenuation in tropical and temperate regions, respectively. For the tropical region, data from the Thaicom 2 and 3 satellites are used, and data from a Japanese communication satellite (CS) are used for the temperate area. Due to the different operating frequencies of the Thaicom 2 and 3 and the CS satellites, the scaling formula from the International Telecommunications Union (ITU) R P.618-12 is used to standardize the data. The Thaicom satellite frequencies of 12.57 (Thaicom 2) and 12.59 (Thaicom 3) GHz in the Ku-band are scaled up to 19.45 GHz, the operating frequency of the CS satellite. Finally, differences of the fade duration and fade slope property in tropical and temperate areas are found and it is confirmed that the rain attenuation effect in tropical areas is more serious than in temperate areas.

  13. 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.

  14. Capacity Fade Analysis of Sulfur Cathodes in Lithium–Sulfur Batteries

    PubMed Central

    Yan, Jianhua; Liu, Xingbo

    2016-01-01

    Rechargeable lithium–sulfur (Li–S) batteries are receiving ever‐increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S‐cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly‐shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li–S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li–S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li–S batteries. PMID:27981001

  15. 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.

  16. 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™.

  17. 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…

  18. The Use of Differential Reinforcement and Fading Time Away Caregiver Child with Separation Anxiety Disorder

    ERIC Educational Resources Information Center

    Flood, William A.; Wilder, David A.

    2004-01-01

    The use of differential reinforcement of other behavior (DRO) and fading of time away from year old boy with Separation Anxiety is illustrated. During baseline, the participant exhibited emotional behavior (i.e., crying, whining, asking to contact parents) as soon as his caregiver left the therapy room. During intervention, the participant was…

  19. Effects of Script Fading on the Abilities of Children with Autism to Reciprocate Information

    ERIC Educational Resources Information Center

    Tedoff, Marc Alan

    2009-01-01

    Teaching communication skills to children with autism is a primary concern because speech and/or language delay characterize autism. One method of teaching verbal communication skills to children with autism is script fading. This study examined the effects of teaching children with autism to exchange information to peers about objects and…

  20. Capacity Fade Analysis of Sulfur Cathodes in Lithium-Sulfur Batteries.

    PubMed

    Yan, Jianhua; Liu, Xingbo; Li, Bingyun

    2016-12-01

    Rechargeable lithium-sulfur (Li-S) batteries are receiving ever-increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S-cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly-shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li-S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li-S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li-S batteries.

  1. 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 ...

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Coded Modulations for Mobile Satellite Communication Channels

    NASA Astrophysics Data System (ADS)

    Rhee, Dojun

    1995-01-01

    The mobile satellite (MSAT) channel is subject to multipath fading, shadowing, Doppler frequency shift, and adjacent channel interference (ACI). Therefore, transmitted signals face severe amplitude and phase distortions. This dissertation investigates various high performance and low decoding complexity coded modulation schemes for reliable voice and data transmissions over the shadowed mobile satellite channel and the Rayleigh fading channel. The dissertation consists of four parts. The first part presents a systematic technique for constructing MPSK trellis coded modulation (TCM) codes for voice transmission over the MSAT channel. The multilevel coding method is used for constructing TCM codes using convolutional codes with good free branch distances as the component codes or using both convolutional and block codes as the component codes. Simulation results show that these codes achieve good coding gains over the uncoded reference system and outperform existing TCM codes with the same decoding complexity. In the second part, using the multilevel coding method, multilevel block coded modulation (BCM) codes are constructed for voice transmission over the MSAT channel. Even though BCM is generally less power efficient than TCM for AWGN channels, BCM has a great potential to compete with TCM in the MSAT channel because of its shorter decoding depth and hence more effective interleaving. Binary Reed -Muller (RM) codes of length up to 32 are used as component codes. Simulation results show that these codes achieve good coding gains over the uncoded reference system and outperform TCM codes with the same decoding complexity. In the third part, a simple and systematic technique for constructing multilevel concatenated BCM schemes for data transmission over the shadowed MSAT channel and the Rayleigh fading channel is presented. These schemes are designed to achieve high-performance or large coding gain with reduced decoding complexity. Construction is based on a

  7. A brief review of ionospheric scintillation fading effects as observed in NASA satellite tracking and data acquisition networks.

    NASA Technical Reports Server (NTRS)

    Golden, T. S.

    1972-01-01

    Discussion of some results of the effects of ionospheric irregularities on NASA satellite tracking and data acquisition operations. Ionospheric scintillation fading produced by irregularities has been observed at 136 MHz (vhf), 400 MHz (uhf), 1550 MHz (L-band) and 1700 to 2200 MHz (S-band). Details of these observations are presented. Vhf scintillation effects are evident in both auroral and equatorial regions. Fading effects decrease with increasing radio frequency in the auroral region. The same frequency dependence for fading is not observed in the equatorial region. Although there is a seasonal and diurnal character to scintillation in the equatorial region, fading effects are usually more severe than in the auroral region for a given radio frequency. Space diversity measurements indicate that reasonable solutions for vhf telemetry problems are available for either region. Space diversity should provide a solution for microwave frequencies as well. Ionospheric fading amplitude for 1700 MHz is relatively small in the auroral region. In the equatorial region amplitude fading levels for 1550-MHz signals from ATS-5 are often much larger than expected. Observations of the Apollo Lunar Surface Experiment Package (ALSEP) operating at 2300 MHz observed near the geomagnetic equator show fading peaks in excess of 15 dB.

  8. 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

  9. 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.

  10. 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.

  11. Channel catfish

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This book chapter provides a comprehensive overview of channel catfish aquaculture. Sections include fish biology; commercial culture; culture facilities; production practices; water quality management; nutrition, feeding and feed formulation; infectious diseases; harvesting and processing; and the...

  12. Mechanosensitive Channels

    NASA Astrophysics Data System (ADS)

    Martinac, Boris

    Living cells are exposed to a variety of mechanical stimuli acting throughout the biosphere. The range of the stimuli extends from thermal molecular agitation to potentially destructive cell swelling caused by osmotic pressure gradients. Cellular membranes present a major target for these stimuli. To detect mechanical forces acting upon them cell membranes are equipped with mechanosensitive (MS) ion channels. Functioning as molecular mechanoelectrical transducers of mechanical forces into electrical and/or chemical intracellular signals these channels play a critical role in the physiology of mechanotransduction. Studies of prokaryotic MS channels and recent work on MS channels of eukaryotes have significantly increased our understanding of their gating mechanism, physiological functions, and evolutionary origins as well as their role in the pathology of disease.

  13. 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.

  14. The role of mechanically induced separator creep in lithium-ion battery capacity fade

    NASA Astrophysics Data System (ADS)

    Peabody, Christina; Arnold, Craig B.

    2011-10-01

    Lithium-ion batteries are well-known to be plagued by a gradual loss of capacity and power which occur regardless of use and can be limiting factors in the development of emerging energy technologies. Here we show that separator deformation in response to mechanical stimuli that arise under normal operation and storage conditions, such as external stresses on the battery stack or electrode expansion associated with lithium insertion/deinsertion, leads to increased internal resistance and significant capacity fade. We find this mechanically induced capacity fade to be a result of viscoelastic creep in the electrochemically inactive separator which reduces ion transport via a pore closure mechanism. By applying compressive stress on the battery structure we are able to accelerate aging studies and identify this unexpected, but important and fundamental link between mechanical properties and electrochemical performance. Furthermore, by making simple modifications to the electrode structure or separator properties, these effects can be mitigated, providing a pathway for improved battery performance.

  15. Disclosing Whole Reaction Pathways of Photochromic 3H-Naphthopyrans with Fast Color Fading.

    PubMed

    Brazevic, Sabina; Sliwa, Michel; Kobayashi, Yoichi; Abe, Jiro; Burdzinski, Gotard

    2017-03-02

    Instantaneous coloration with large absorbance and quick color fading in the dark are desired properties for thermally reversible photochromic compounds. In the case of naphthopyran derivatives, which have been employed to commercial ophthalmic lenses, the quick color fading has been recently achieved by suppression of the generation of the transoid-trans (TT) form by steric hindrance of bulky substituents. However, there are still open questions whether the steric hindrance decreases the photochromic reaction efficiency, which is a crucial problem for industrial applications. Herein, we apply a wide range of electronic and vibrational time-resolved spectroscopies and reveal that the photochromic reaction yields of the naphthopyrans with bulky substituents are almost comparable (∼0.7) to that of nonsubstituted naphthopyran. The suppression of the formation of the TT form and the effect of solvent polarity on the photodynamics are systematically investigated. These findings are important for fundamental photochemistry and developing naphthopyran-based optimal photofunctional materials.

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

    PubMed

    Saito, Mitsunori; Nishimura, Tatsuya; Hamazaki, Takamasa

    2015-10-05

    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.

  17. 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.

  18. Experimental and theoretical studies of perceptible color fading of decorative paints consisting of mixed pigments

    NASA Astrophysics Data System (ADS)

    Auger, Jean-Claude; McLoughlin, Daragh

    2017-01-01

    We study the color fading of paints films composed of mixtures of white rutile titanium dioxide and yellow arylide pigments dispersed in two polymer binders at different volume concentrations. The samples were exposed to ultraviolet radiations in an accelerated weathering tester during three weeks. The measured patterns in color variations appeared to be independent of the chemistry of the binders. We then developed a theoretical framework, based on the Radiative transfer Equation of light and the One Particle T-Matrix formalism to simulate the color fading process. The loss of color is correlated to the progressive decrease of the original colored pigment volume-filling fraction as the destructive UV radiations penetrate deeper into the films. The calculated patterns of color variations of paints film composed by mixtures of white pigments with yellow Cadmium Sulfate (CdS) and red Cerium Sulfide (Ce2S3) pigments showed the same trend as that seen experimentally.

  19. 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.

  20. Using audio script fading and multiple-exemplar training to increase vocal interactions in children with autism.

    PubMed

    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 occurring relevant stimuli. In this study, 4 boys with autism were taught to initiate a conversation in the presence of toys through the use of a script and script-fading procedure. Training with multiple categories and exemplars of toys was used to increase the likelihood of generalization of vocal interactions across novel toys. A multiple-probe design across participants was used to assess the effects of these procedures. The intervention successfully brought interactions by children with autism under the control of relevant stimuli in the environment. Future research pertaining to the specific implementation of these procedures (e.g., fading, script placement, participant characteristics) is discussed.

  1. A reverberation chamber for rodents' exposure to wideband radiofrequency electromagnetic fields with different small-scale fading distributions.

    PubMed

    Li, Congsheng; Yang, Lei; Lu, Bingsong; Xie, Yi; Wu, Tongning

    2016-01-01

    A reverberation chamber (RC) is realized for the rodents' in vivo exposure to electromagnetic fields (EMFs) with various small-scale fading characteristics. Its performance is evaluated to ensure the exposure experiments from 0.85 to 2.60 GHz. By different configurations, line-of-sight and non-line-of-sight exposures can be established. The measured electric field in the RC is analyzed to determine its statistical distribution. We accordingly reconstruct the EMF environment by numerical methods. Simulations are carried to compare the dosimetric variability due to different small-scale fading characteristics. It demonstrates that the surveyed fading distribution will not change the specific absorption rate in the rats. The possibility to reproduce the realistic multi-reflective EMF environment by adjusting the structures of the RC is discussed. It is the first reported in vivo exposure system aiming to provide the EMF exposure with different small-scale fading distributions.

  2. 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.

  3. 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.

  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 Analysis of ORCA Data Beam at NTTR and Pax River

    DTIC Science & Technology

    2010-08-01

    FINAL REPORT: FADE ANALYSIS OF ORCA DATA BEAM AT NTTR AND PAX RIVER UCF DARPA Project ID: 16296051 HR0011-08-C-0111 R. Crabbs, D. Wayne, T ...1 , 1 , 1 1 ~ 30 40 50 60 Range (km) T ’ I — T 1 , — . | 0 PAX River...losses. Thus, the mean PIF is calculated from the relation PIF = rop,PIB/Aiiy ’ 4A SR t - (2) where SRf is the Strehl ratio associated with the

  7. Transcriptome Analysis Reveals Candidate Genes Related to Color Fading of ‘Red Bartlett’ (Pyrus communis L.)

    PubMed Central

    Wang, Zhigang; Du, Hong; Zhai, Rui; Song, Linyan; Ma, Fengwang; Xu, Lingfei

    2017-01-01

    The red color of fruit is an attractive plant trait for consumers. Plants with color-faded fruit have a lower commercial value, such as ‘Red Bartlett’ pears (Pyrus communis L.) that have dark-red fruit in the early stages of fruit development that subsequently fade to red-green at maturity. To identify the reason for color fading, we first analyzed the anthocyanin content of peel from ‘Red Bartlett,’ which displays the color fading phenomenon, and ‘Starkrimson,’ which has no color fading. Results showed that the anthocyanin content of ‘Red Bartlett’ peel decreased significantly late in fruit development, while in ‘Starkrimson’ there was no significant decrease. Next, RNA-Sequencing was used to identify 947 differentially expressed genes (DEGs) between ‘Red Bartlett’ and ‘Starkrimson.’ Among them, 471 genes were upregulated and 476 genes were downregulated in ‘Red Bartlett’ at the late development stage relative to ‘Starkrimson.’ During ‘Red Bartlett’ color fading, the structural gene LDOX and six GST family genes were downregulated, while FLS, LAC, POD, and five light-responding genes were significantly upregulated. Additionally, 45 genes encoding transcription factors MYB, bHLH, WRKY, NAC, ERF, and zinc finger were identified among 947 DEGs. Changes in the expression of these genes may be responsible for the decrease in anthocyanin accumulation in ‘Red Bartlett’ fruit. Taken together, this study demonstrated that color fading of ‘Red Bartlett’ was closely linked to reduced anthocyanin biosynthesis, increased anthocyanin degradation and suppression of anthocyanin transport. It also provided novel evidence for the involvement of light signals in the color fading of red-skinned pears.

  8. Capacity fade of Sony 18650 cells cycled at elevated temperatures. Part I. Cycling performance

    NASA Astrophysics Data System (ADS)

    Ramadass, P.; Haran, Bala; White, Ralph; Popov, Branko N.

    The capacity fade of Sony 18650 Li-ion cells increases with increase in temperature. After 800 cycles, the cells cycled at RT and 45 °C showed a capacity fade of 30 and 36%, respectively. The cell cycled at 55 °C showed a capacity loss of about 70% after 490 cycles. The rate capability of the cells continues to decrease with cycling. Impedance measurements showed an overall increase in the cell resistance with cycling and temperature. Impedance studies of the electrode materials showed an increased positive electrode resistance when compared to that of the negative electrode for cells cycled at RT and 45 °C. However, cells cycled at 50 and 55 °C exhibit higher negative electrode resistance. The increased capacity fade for the cells cycled at high temperatures can be explained by taking into account the repeated film formation over the surface of anode, which results in increased rate of lithium loss and also in a drastic increase in the negative electrode resistance with cycling.

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

    SciTech Connect

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

    2016-05-06

    Lithium-ion batteries utilizing manganese based cathodes have received considerable interest in recent years for their lower cost and favorable environmental friendliness relative to their cobalt counterparts. However, Li-ion batteries using manganese based cathodes and graphite anodes suffer from severe capacity fading at higher operating temperature. In this article, we report on an astute investigation into 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 inner most solid electrolyte interphase (SEI) 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.

  10. Capacity fade in thin-film lithium-V{sub 2}O{sub 5} cells

    SciTech Connect

    Kwak, B.S.; Bates, J.B.; Hart, F.X.

    1996-01-01

    Capacity fade with cycling of thin-film rechargeable Li/Lipon/V{sub 2}O{sub 5} cells, formed as electrochromic mirrors with ITO current collectors, has been studied by optical and impedance spectroscopy and extended cycling experiments. An irreversible decrease in the reflectivity observed in cells cycled between 3.6 to 1.5 V was attributed to a roughening of the Li surface at the Li-Lipon interface. Although the consequent loss of contact area might be the source of increasing cell resistance responsible for the capacity fade, this possibility was ruled out because of the large variability observed in the cycling performance of cells with different cathodes and the constancy of the reflectivity when the cutoff voltage was increased to 2.5 V. It was concluded from the analysis of impedance data that a decrease in Li{sup +} ion diffusivity in the cathode and the cathode-electrolyte interface with cycling is the major cause of capacity fade.

  11. Pre- and postsynaptic mechanisms involved in tetanic fade induced by pancuronium in the isolated rat muscle.

    PubMed

    Gallacci, M; Oliveira, A C

    1994-10-01

    The mechanisms underlying the fade of the tetanic contraction induced by pancuronium were studied in vitro by means of myographical and electrophysiological techniques in the extensor digitorum longus muscle of the rat. Pancuronium (0.5 mumol/l) induced a complete fade of the tetanic contraction while leaving the twitch unaffected. At the same concentration it decreased the amplitude and increased the tetanic rundown of trains of endplate potentials (e.p.ps) evoked in the frequency of 50 Hz. The electrophysiological changes induced by pancuronium were due to decreases in both quantal sizes and quantal contents of the e.p.ps. The former effect was the result of a postsynaptic competitive action and the latter of a presynaptic inhibitory action of that compound. The decrease in quantal content affected the e.p.ps starting from the first in the train and became larger during the generation of the sequence of e.p.ps. This intensified their tetanic rundown. It is concluded that the fade of the tetanic contraction induced by pancuronium is due to a summation of pre- and postsynaptic actions and, therefore, not only to an increase in the tetanic rundown of e.p.ps. Possible explanations for the distinct abilities of neuromuscular blockers in affecting tetani and twitches in a differential manner are also discussed.

  12. An algorithm for pre- and post-irradiation fade in the Thermo 8802 LiF:Mg,Ti thermoluminescent dosimeter.

    PubMed

    Hill, Carolyn D

    2005-05-01

    The diminished response of thermoluminescent phosphors over time is a well-documented challenge to thermoluminescent dosimetry. Wide ranges in fading rates for various phosphor types have been reported, making it necessary for many external dosimetry programs to perform individual studies on thermoluminescent fade. Sandia National Laboratories currently uses the Thermo 8802 LiF:Mg,Ti thermoluminescent dosimeter (TLD) in its personnel external dosimetry program. Doses received in the field are calculated by applying a fade algorithm published by the manufacturer to TLD readings. Since the algorithm was established by characterizing the diminished response of a TLD similar to the 8802, Sandia chose to model its fade study after the analysis done by Thermo. As a result, the parameters of each experiment were comparable, and data from the two studies were compared to determine whether or not the current algorithm should be modified specifically for use at Sandia. Cards were irradiated using an internal Sr/Y source, and pre- and post-irradiation fading rates were monitored over a period of 18 wk. While significant fading was demonstrated, results closely matched those found in the original Thermo study.

  13. 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

  14. 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.

  15. Performance of Improved Channel Allocation for Multicarrier CDMA with Adaptive Frequency Hopping and Multiuser Detection

    DTIC Science & Technology

    2008-08-29

    SECURITY CLASSIFICATION OF: Subchannel allocation for the reverse link of multicarrier code-division multiplex-access (MC-CDMA) system with adaptive...Triangle Park, NC 27709-2211 15. SUBJECT TERMS subchannel allocation, fading channels, CDMA Tao Jia, Alexandra Duel-Hallen North Carolina State University... Subchannel allocation for the reverse link of multicarrier code-division multiplex-access (MC-CDMA) system with adaptive frequency hopping (AFH) is

  16. Effects of the Wireless Channel, Signal Compression and Network Architecture on Speech Quality in Voip Networks

    DTIC Science & Technology

    2007-06-01

    coding and compression on the received speech quality. Both simulation and experimentation are conducted using Matlab code and Speex software and...using Matlab code and Speex software and across commercial VoIP networks. Simulation shows that fading channel parameters can heavily affect the...experimentation. Simulation is implemented using Matlab and Speex software , and the experiments are conducted on commercial VoIP networks. xvi Simulation

  17. 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.

  18. Equalization of Time-Varying Dispersive Channels via Sequence Estimation.

    DTIC Science & Technology

    1983-07-13

    Vol. 4, Academic Press 1975. [8] F. R. Magee and J. G. Proakis , "Adaptive Maximum-Likelihood Sequence Estimation for Digital Signaling in the Presence...courses of action which can be pursued to maintain reliable comunications over the selective fading channel are; 1) to reduce the maxinum information...and the complex (I,Q) received signal samples are given by rk =Z c(tj)h(t- tj) + n,(tk) + nQ(tk) (2) 4. where the sumnation is the digital convolution

  19. 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.

  20. Frequency-Domain QR-Decomposed and Equalized MLD for Single-Carrier MIMO Systems over Multipath Fading Channels

    NASA Astrophysics Data System (ADS)

    Miyatani, Tetsuhiko

    This letter describes a new QR-decomposition maximum likelihood detector that is combined with frequency-domain equalization for single-carrier transmission based multiple-input multiple-output systems. By utilizing the equalized substreams to adjust the frequency selectivity in corresponding substreams in subsequent stages, the packet error rate performances of the proposed detector is superior to that of the minimum mean squared error receiver by a factor of the receive antenna diversity gain.

  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. 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

  3. Starburst Channels

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1

    Translucent carbon dioxide ice covers the polar regions of Mars seasonally. It is warmed and sublimates (evaporates) from below, and escaping gas carves a numerous channel morphologies.

    In this example (figure 1) the channels form a 'starburst' pattern, radiating out into feathery extensions. The center of the pattern is being buried with dust and new darker dust fans ring the outer edges. This may be an example of an expanding morphology, where new channels are formed as the older ones fill and are no longer efficiently channeling the subliming gas out.

    Observation Geometry Image PSP_003443_0980 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 21-Apr-2007. The complete image is centered at -81.8 degrees latitude, 76.2 degrees East longitude. The range to the target site was 247.1 km (154.4 miles). At this distance the image scale is 24.7 cm/pixel (with 1 x 1 binning) so objects 74 cm across are resolved. The image shown here has been map-projected to 25 cm/pixel. The image was taken at a local Mars time of 04:52 PM and the scene is illuminated from the west with a solar incidence angle of 71 degrees, thus the sun was about 19 degrees above the horizon. At a solar longitude of 223.4 degrees, the season on Mars is Northern Autumn.

  4. Rain fade in Ku-band VSAT networks - A design consideration

    NASA Astrophysics Data System (ADS)

    Raust, Eric H.

    The components of a Very Small Aperture Terminal (VSAT) network are shown to determine the effect that rainfall has on Ku-band satellite communications. This paper considers the effect of the signal attenuation caused by rain as predicted by a well known rain fade model. The result, of considering the highest rain attenuations experienced is related to both transmission availabilities and signal margins. The results of link calculations are tabulated for typical network designs. These results show that proper selection of the VSAT's components and the satellite transponder power can all but eliminate rain outages while maintaining the economics of a Ku-band VSAT network.

  5. 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.

  6. Phase Sequence Estimation for Laser Line-Scan Imagery in the Presence of Rayleigh Fading.

    DTIC Science & Technology

    1979-12-01

    Warning Radar for Det 4, 14 Missle Warning Squadron, Mt. Laguna AFS, California. In May 1975, he was assigned to the 1961st Communications Group, Clark Air...unlimited Preface This study was prompted by a phase estimation problem of a fading signal in a laser line-scan imagery system . The sys- tem is sponsored by...114 ii I List of Figures Figure 1 Geometry of the Laser Line-scan System . . . . .. 3 2. Block Diagram of Laser Line-scan Imagery System . 4 3

  7. 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.

  8. 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%.

  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. 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.

  11. Mechanisms for capacity fading in the NiH2 cell and its effects on cycle life

    NASA Technical Reports Server (NTRS)

    Zimmerman, Albert H.

    1993-01-01

    During recent years there have been a number of instances where the capacity of nickel hydrogen battery cells has proven to be unstable during storage. The capacity losses seen after periods of cell or battery storage have typically varied from only a small amount of fading, up to about 30 percent of the total cell capacity. Detailed studies into the root causes for such fading have been carried out in a number of instances. This report provides an overview of the different mechanisms that have been found to be responsible for such capacity fading in nickel hydrogen cells, and summarizes the presently available data on how each responsible mechanism affects ultimate cell cycle life.

  12. Multiphysics modeling of lithium ion battery capacity fading process with solid-electrolyte interphase growth by elementary reaction kinetics

    NASA Astrophysics Data System (ADS)

    Xie, Yuanyuan; Li, Jianyang; Yuan, Chris

    2014-02-01

    A pseudo two-dimensional mathematical model is developed for a lithium ion battery, integrating the elementary reaction based solid-electrolyte interphase (SEI) growth model with multiple transport processes. The model is validated using the experimental data. Simulation results indicate that the operating temperature has great effect on the SEI layer generation and growth. Under different charging-discharging rates, it is found that high charging-discharging rate can intensify the battery capacity fading process. Different cooling conditions are then applied and show that enhanced surface convective cooling condition can effectively slow down the battery capacity fading. After that, the effect of electrolyte salt concentration and exchange current density are studied. It is found that raising the electrolyte salt concentration can improve the diffusion property of lithium ions, and stabilize the battery performance under lithium ion consumption induced resistance rising. It also suggests that improving exchange current density could greatly decrease the lithium ion battery capacity fading.

  13. 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.

  14. Dynamic Channel Allocation

    DTIC Science & Technology

    2003-09-01

    7 1 . Fixed Channel Allocation (FCA) ........................................................7 2. Dynamic Channel ...19 7. CSMA/CD-Based Multiple Network Lines .....................................20 8. Hybrid Channel Allocation in Wireless Networks...28 1 . Channel Allocation

  15. 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

  16. 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

  17. Illusory color mixing upon perceptual fading and filling-in does not result in 'forbidden colors'.

    PubMed

    Hsieh, P-J; Tse, P U

    2006-07-01

    A retinally stabilized object readily undergoes perceptual fading. It is commonly believed that the color of the apparently vanished object is filled in with the color of the background because the features of the filled-in area are determined by features located outside the stabilized boundary. Crane, H. D., & Piantanida, T. P. (1983) (On seeing reddish green and yellowish blue. Science, 221, 1078-1080) reported that the colors that are perceived upon full or partial perceptual fading can be 'forbidden' in the sense that they violate color opponency theory. For example, they claimed that their subjects could perceive "reddish greens" and "yellowish blues." Here we use visual stimuli composed of spatially alternating stripes of two different colors to investigate the characteristics of color mixing during perceptual filling-in, and to determine whether 'forbidden colors' really occur. Our results show that (1) the filled-in color is not solely determined by the background color, but can be the mixture of the background and the foreground color; (2) apparent color mixing can occur even when the two colors are presented to different eyes, implying that color mixing during filling-in is in part a cortical phenomenon; and (3) perceived colors are not 'forbidden colors' at all, but rather intermediate colors.

  18. Coding techniques to mitigate fading on free-space optical communication links

    NASA Astrophysics Data System (ADS)

    Henniger, Hennes; Epple, Bernhard; Milner, Stuart D.; Davis, Christopher C.

    2008-08-01

    Free-space directional communication links (FSO) experience short-term link outages or fades because of atmospheric turbulence, and longer term link outages because of obscuration resulting from either atmospheric conditions, beam pointing errors, or temporary line-of-sight obstructions for links from mobile or static nodes. Various approaches can be used to mitigate these effects. Physical-layer techniques, such as dynamic thresholding, time delayed diversity, and data encoding can significantly reduce the effects of short term (millisecond scale) outages caused by deep turbulenceinduced fades. Outages on a longer term (second scale) producing large data loss can be mitigated by packet-layer largeblock, error protection techniques. In this paper, we will first introduce physical-layer mitigation techniques. Second we present experimental data comparing the latencies and throughput of different means of packet-based error protection techniques. We will discuss the influence of error protection techniques to quality of service issues like error probability and delay and further compare this with service requirements given by the application.

  19. 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.

  20. 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.

  1. 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.

  2. Modeling The Atmosphere As An Unguided Optical Communications Channel

    NASA Astrophysics Data System (ADS)

    Nuber, Raymond M.

    1989-07-01

    Due to the increasing number of applications for optical communications, methods such as computer simulation are needed for the performance analysis of these systems. The objective of this paper is to propose a system level model for simulating the Earth's atmosphere as an unguided optical communications channel. The major degradations in received optical intensity introduced by the atmosphere are scintillation, beam spreading, beam wander, and atmospheric transmissivity. The model presented here considers scintillation and beam wander to impose random fading in the received signal while beam spreading is a constant loss in intensity. Atmospheric transmissivity is treated as a filter-like channel transfer function. Relationships for the parameters of the model are given in terms of parameters which characterize the optical link. Also included is a description of an implementation of the model.

  3. 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

  4. 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.

  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. 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…

  8. 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…

  9. 78 FR 42818 - SafetyAlert: Safety Alert: Risks Associated With Liquid Petroleum (LP) Gas Odor Fade

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-07-17

    ... a manual injection process, quality control checks should be conducted to ensure that the requisite... this fact and that persons filling these tanks implement appropriate quality control measures to ensure that potential odorant fade is adequately addressed. Such quality control measures will ensure...

  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. 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…

  12. 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…

  13. 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.

  14. 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…

  15. 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.

  16. Identify capacity fading mechanism in a commercial LiFePO 4 cell

    NASA Astrophysics Data System (ADS)

    Dubarry, Matthieu; Liaw, Bor Yann

    The capacity fading of an 18650 LiFePO 4-based lithium ion cell was studied using the dynamic stress test (DST) schedule in a cycle life evaluation. Intermittent reference performance tests were conducted to quantify capacity loss and peak power capability degradation with cycle number to the end-of-life. An incremental capacity analysis was applied to identify various contributions to capacity loss, whereas the open circuit voltage measurements were utilized to trace the correct state of charge as the cell degrades in order to accurately correlate the capacity degradation with SOC. Our non-invasive, in situ analyses are in general consistent with current understanding of the degradation mechanism in this chemistry derived from post-mortem analysis. Loss of lithium inventory is the main cause of capacity degradation, in addition to the loss of active materials. The degree of under-discharge and under-charge is quite minimal under the test protocol.

  17. Diagnosis of power fade mechanisms in high-power lithium-ion cells

    NASA Astrophysics Data System (ADS)

    Abraham, D. P.; Liu, J.; Chen, C. H.; Hyung, Y. E.; Stoll, M.; Elsen, N.; MacLaren, S.; Twesten, R.; Haasch, R.; Sammann, E.; Petrov, I.; Amine, K.; Henriksen, G.

    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.

  18. 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.

  19. The Fading of the Narrow-Line Region in 3C 390.3: Erratum

    NASA Astrophysics Data System (ADS)

    Clavel, J.; Wamsteker, W.

    1988-07-01

    The Letter "The Fading of the Narrow-Line Region in 3C 390.3" by J. Clavel and W. Wamsteker (Ap. J. [Letters], 320, L9 [1987]) contains an error in the last two sentences of section IIIb: The density we compute for the broad line region (BLR) gas is wrong by a factor of 10 exactly and should read 10^11^ cm^-3^ instead of 10^10^. Such a density is about 30 times larger than the canonical 10^9.5^ cm^-3^ value generally used in model calculations but similar to the density inferred for the BLR in NGC 4151 by J. Clavel et al. (Ap. J., 321, 251 [1987]). The authors are grateful to Paolo Padovani from STScI for bringing this error to their attention.

  20. 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.

  1. Noise adaptive fading Kalman filter for free-space laser communication beacon tracking.

    PubMed

    Li, Lixing; Huang, Yongmei; Wang, Qiang; Yang, Fasheng

    2016-10-20

    We proposed a prediction algorithm for laser communication pointing, acquisition, and tracking (PAT) subsystems in order to further improve PAT accuracy and reduce the effect of processing delay. In terms of this prediction algorithm, a fading Kalman filter is employed, with the observation noise obtained by the gray value distribution of the laser images. Moreover, to better fit the dynamics of a laser target, the two-stage dynamic model has been chosen as the state transition model for Kalman filtering. In addition, the two-stage dynamic model has been modified by accommodating its form to a change of time lag, thereby compensating the effect of time delay. A series of horizontal path (17 km) experiments under different atmospheric conditions were conducted in the fields. According to the experimental results, the algorithm we proposed could effectively reduce the tracking error and improve pointing accuracy.

  2. 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

  3. 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

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Eukaryotic mechanosensitive channels.

    PubMed

    Arnadóttir, Jóhanna; Chalfie, Martin

    2010-01-01

    Mechanosensitive ion channels are gated directly by physical stimuli and transduce these stimuli into electrical signals. Several criteria must apply for a channel to be considered mechanically gated. Mechanosensitive channels from bacterial systems have met these criteria, but few eukaryotic channels have been confirmed by the same standards. Recent work has suggested or confirmed that diverse types of channels, including TRP channels, K(2P) channels, MscS-like proteins, and DEG/ENaC channels, are mechanically gated. Several studies point to the importance of the plasma membrane for channel gating, but intracellular and/or extracellular structures may also be required.

  11. Visible Persistence of Single-Transient Random Dot Patterns: Spatial Parameters Affect the Duration of Fading Percepts

    PubMed Central

    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. PMID:26348616

  12. Capacity of UWB wireless channel for neural recording systems.

    PubMed

    El Khaled, Mohamad; Bahrami, Hadi; Fortier, Paul; Gosselin, Benoit; Rusch, Leslie Ann

    2014-01-01

    Ultra wide-band (UWB) short-range communication systems are valuable in medical technology, particularly for implanted devices, due to their low-power consumption, low cost, small size and high data rates. Monitoring of neural responses in the brain requires high data rate if we target a system supporting a large number of sensors. In this work, we are interested in the evaluation of the capacity of the ultra wide-band (UWB) channel that we could exploit using a realistic model of the biological channel. The channel characteristics are examined under two scenarios that are related to TX antenna placements. Using optimal power spectrum allocation (OPSA) at the transmitter side, we have computed this capacity by taking into account the fading characteristics of the channel. The results show the pertinence of the optimal power spectrum allocation for this type of channel. An improvement by a factor of 2 to 3 over a uniform power spectrum allocation (UPSA) when the SNR <; 0 dB was obtained. When the SNR is > 40 dB, both approaches give similar results. Antennas placement is examined under two scenarios having contrasting power constraints.

  13. Time-Frequency Based Channel Estimation for High-Mobility OFDM Systems-Part I: MIMO Case

    NASA Astrophysics Data System (ADS)

    Önen, Erol; Akan, Aydın; Chaparro, LuisF

    2010-12-01

    Multiple-input multiple-output (MIMO) systems hold the potential to drastically improve the spectral efficiency and link reliability in future wireless communications systems. A particularly promising candidate for next-generation fixed and mobile wireless systems is the combination of MIMO technology with Orthogonal Frequency Division Multiplexing (OFDM). OFDM has become the standard method because of its advantages over single carrier modulation schemes on multipath, frequency selective fading channels. Doppler frequency shifts are expected in fast-moving environments, causing the channel to vary in time, that degrades the performance of OFDM systems. In this paper, we present a time-varying channel modeling and estimation method based on the Discrete Evolutionary Transform to obtain a complete characterization of MIMO-OFDM channels. Performance of the proposed method is evaluated and compared on different levels of channel noise and Doppler frequency shifts.

  14. The Psychology of Channeling.

    ERIC Educational Resources Information Center

    Corey, Michael A.

    1988-01-01

    Theoretically analyzes phenomenon of channeling from perspective of C. G. Jung's analytic psychology. Hypothesizes that contact with otherworldly spiritual beings claimed by channelers is actually projected contact with contents of channeler's own unconscious mind. Suggests that channelers seek more constructive ways of contacting their…

  15. 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.

  16. Modifying the Turbo Decoder for DVC over Wireless Channels

    NASA Astrophysics Data System (ADS)

    Weerakkody, Rajitha; Fernando, Anil; M. Kondoz, Ahmet

    Distributed Video Coding (DVC) is an emerging video coding approach, particularly attractive due to its flexibility to implement low complex encoders. This feature could be very effectively utilized in a number of video sensor based application scenarios. However, DVC is still in the process of development and currently available codec implementations are based on a number of hypothetical models and assumptions. In DVC, the effects of noise and fading on the compressed payload (parity bit stream) in real video communications and the resultant modified channel model scenario have not been discussed in literature. In this paper, a solution to the above problem in turbo coding based DVC is discussed incorporating a novel dual channel model for the maximum a-posteriori (MAP) algorithm for turbo decoding. The simulations for AWGN and wireless channels at different group of picture (GOP) sizes show that the proposed algorithm improves the rate distortion performance compared to the existing decoding algorithm. It also outperforms the H.264/AVC I-P-I-P codec (v10.1/baseline profile); particularly at low Signal to Noise Ratio (SNR) levels of the channel, thus enabling DVC as a viable and efficient option for video communications.

  17. 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.

  18. Power fading mitigation of 40-Gbit/s 256-QAM OFDM carried by colorless laser diode under injection-locking.

    PubMed

    Tsai, Cheng-Ting; Chi, Yu-Chieh; Lin, Gong-Ru

    2015-11-02

    The pre-compensation on power fading effect of a colorless laser diode (CLD) carried 40-Gbit/s 256-QAM OFDM transmission during 25-km is demonstrated. By offsetting the DC bias to thrice the threshold (I(th)) and increasing the injection to 0 dBm, the CLD not only enhances its coherence but also suppresses modulation throughput declination and reduces the relative intensity related noise floor to -50 dBm. Modeling the receiving power of the delivered 256-QAM OFDM subcarriers is established, indicating that raising the bias to 3I(th) down-shifts the power fading induced notch to 8.8 GHz. This further degrades the OFDM subcarrier peak power by -2.9 dB after 25-km transmission, and the corresponded signal-to-noise ratio (SNR), error vector magnitude (EVM) and bit-error-rate (BER) are 26.1 dB, 4.9% and 6.5 × 10(-3), respectively. Pre-leveling the OFDM subcarrier as well as the modulation throughput effectively compromises the over-bias enlarged power fading to promote transmission. With a pre-leveled power slope of 1.5 dB/GHz for 256-QAM OFDM data, the modulation throughput declination of the high biased CLD significantly mitigates under BtB transmission, enabling the receiving sensitivity at -7.2 dBm with SNR, EVM and BER of 29.9 dB, 3.1% and 1.5 × 10(-4), respectively. Increasing the pre-leveling slope to 3.2 dB/GHz minimizes the fiber dispersion induced power fading, which improves the receiving SNR, EVM and BER to 27.4 dB, 4.2% and 2.6 × 10(-3), respectively, with receiving sensitivity of -3 dBm and power penalty of 4.2 dB after 25-km SMF transmission.

  19. 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.

  20. Comparison of the capacity fade of Sony US 18650 cells charged with different protocols

    NASA Astrophysics Data System (ADS)

    Sikha, G.; Ramadass, P.; Haran, B. S.; White, R. E.; Popov, Branko N.

    A new varying current decay (VCD) protocol, which charges the Li-ion battery at a faster rate, was developed. The performance of the battery charged using the VCD protocol was compared with the performance of batteries charged with conventional constant current-constant voltage (CC-CV) and constant voltage (CV) protocols. The destructive physical analysis tests at the end of 150 cycles indicated higher impedance for the cells cycled using the VCD protocol compared to the cell charged using the conventional (CC-CV) mode. The observed increase of the impedance was due to a small increase of the potential above the cut-off value of 4.2 for short times. A complete capacity fade material balance as a function of number of cycles was performed in order to account for the total capacity loss due to different charging protocols used. The loss of primary active material (Li +), the secondary active material (LiCoO 2/carbon) and the rate capability losses were determined for Sony US 18650 Li-ion cells and compared for different charging protocols.

  1. Critical anomalies of alkaline fading of phenolphthalein in the critical solution of 2-butoxyethanol + water

    NASA Astrophysics Data System (ADS)

    Du, Zhongyu; Yin, Handi; Hao, Zhiguo; Zheng, Peizhu; Shen, Weiguo

    2013-12-01

    We have used three-wavelength UV-spectrophotometry to study the reaction of the alkaline fading of phenolphthalein in the critical solution of 2-butoxyethanol + water. It was found that when the temperature was far away from the critical point, the values of the natural logarithm of the rate constant k and the natural logarithm of the chemical equilibrium K determined in our experiments had good linear relationships with the reciprocal of temperature, which served as the backgrounds and were used for correcting k and K in the critical region. The critical slowing down of the reaction and the critical anomaly of the chemical equilibrium were detected near the critical point. The value of the critical exponent characterizing the slowing down effect of the reaction rate was obtained to be 0.156, which was close to the value 0.11 associated with the heat capacity divergence and agreed with the theoretical prediction. The experimental result also confirmed the theoretical prediction of 0.11 for the critical exponent characterizing the weak divergence of the singularity of the chemical equilibrium.

  2. Satellite triangulation of thunderstorms, from fading radio fields synchronously recorded on two orthogonal antennas

    NASA Astrophysics Data System (ADS)

    Jacobson, Abram R.; Shao, Xuan-Min; Holzworth, Robert H.

    2011-12-01

    Single-satellite observations of lightning radio emissions normally do not independently provide useful thunderstorm location. The scientific value of these radio waveform recordings is greatly enhanced by knowing at least the approximate location of the source thunderstorm. Since the Very High Frequency radio emissions from lightning are always broadband and usually incoherent, radio interferometry is an obvious approach to direction-finding the source. However, radio-interferometry requires separated, deployed antennas, and for decametric radio waves, success with interferometric direction-finding on a satellite has not yet been reported. We describe a method for approximate location of source thunderstorms, using the statistical fading of the received electric field on two orthogonal, but co-located, antennas. The method is based on previous work geolocating polarized sources, and we show that it can be adapted efficiently to unpolarized radio fields, which constitute the majority of lightning emissions. We implement the method with dual-antenna radio recordings from the FORTE satellite, and demonstrate its capabilities using a wide variety of radio data.

  3. Fading of alizarin and related artists's pigments by atmospheric ozone: reaction products and mechanisms

    SciTech Connect

    Grosjean, D.; Whitmore, P.M.; De Moor, C.P.; Cass, G.R.; Druzik, J.R.

    1987-07-01

    The colorants alizarin and Alizarin Crimson (a calcium-aluminum lake pigment) and their simple structural homologue anthraquinone were deposited on silica gel, cellulose, and Teflon substrates and exposed in the dark to ozone in purified air (approx.0.4 ppm O/sub 3/ for 95 days and approx.10 ppm O/sub 3/ for 18-80 h). Exposed and control samples were analyzed by mass spectrometry. Alizarin Crimson reacted with ozone on all substrates, yielding phthalic acid (major), benzoic acid (minor), and other minor and unidentified products. Anthraquinone did not react with ozone irrespective of conditions. Alizarin did not react on Teflon or cellulose but reacted on silica gel to yield phthalic acid (major) and other products. A chemical mechanism responsible for the fading of these alizarin-related colorants by ozone is suggested that is consistent with the products distribution, the observed reactivity sequence, and the observed substrate-specific effects. The possible application of this work to predicting the ozone fastness of other alizarin-related pigments is discussed briefly. 33 references, 5 figures.

  4. 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.

  5. Delayed diversity for fade resistance in optical wireless communications through turbulent media

    NASA Astrophysics Data System (ADS)

    Trisno, Sugianto; Smolyaninov, Igor I.; Milner, Stuart D.; Davis, Christopher C.

    2004-10-01

    Atmospheric turbulence causes fluctuations in both the intensity and phase of the received signal in an optical wireless communication link. These fluctuations, often referred to as scintillation noise, lead to signal fading, which increase bit errors in digital communication links using intensity modulation and direct detection. The performance of an optical link can be improved by the use of a time delayed diversity technique, which takes advantage of the fact that the atmospheric path from transmitter to receiver is statistically independent for time intervals beyond the correlation time of the intensity fluctuations. We have designed and constructed a prototype optical wireless system using this scheme. Bit-error-rate measurements have been used to characterize the link performance for different delay periods under conditions of controlled simulated turbulence. It has been determined that link performance improves significantly, especially in strong turbulence. In addition, we have implemented orthogonal polarization modulation, which works especially well in optical wireless systems. In contrast to fiber optic communications, the polarization state of a laser beam is well preserved on a free space optical path.

  6. Autonomous Preference-Aware Information Services Integration for High Response in Integrated Faded Information Field Systems

    NASA Astrophysics Data System (ADS)

    Lu, Xiaodong; Mori, Kinji

    The market and users' requirements have been rapidly changing and diversified. Under these heterogeneous and dynamic situations, not only the system structure itself, but also the accessible information services would be changed constantly. To cope with the continuously changing conditions of service provision and utilization, Faded Information Field (FIF) has been proposed, which is a agent-based distributed information service system architecture. In the case of a mono-service request, the system is designed to improve users' access time and preserve load balancing through the information structure. However, with interdependent requests of multi-service increasing, adaptability and timeliness have to be assured by the system. In this paper, the relationship that exists among the correlated services and the users' preferences for separate and integrated services is clarified. Based on these factors, the autonomous preference-aware information services integration technology to provide one-stop service for users multi-service requests is proposed. As compared to the conventional system, we show that proposed technology is able to reduce the total access time.

  7. 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.

  8. 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.

  9. Modeling the Gamma-Ray Emission in the GALACTIC CENTER with a Fading Cosmic-ray Accelerator

    NASA Astrophysics Data System (ADS)

    Liu, Ruo-Yu; Wang, Xiang-Yu; Prosekin, Anton; Chang, Xiao-Chuan

    2016-12-01

    Recent HESS observations of the ∼200 pc scale diffuse gamma-ray emission from the central molecular zone (CMZ) suggest the presence of a PeV cosmic-ray accelerator (PeVatron) located in the inner 10 pc region of the Galactic center. Interestingly, the gamma-ray spectrum of the point-like source (HESS J1745-290) in the Galactic center shows a cutoff at ∼10 TeV, implying a cutoff around 100 TeV in the cosmic-ray proton spectrum. Here we propose that the gamma-ray emission from the inner and the outer regions may be explained self-consistently by run-away protons from a single yet fading accelerator. In this model, gamma-rays from the CMZ region are produced by protons injected in the past, while gamma-rays from the inner region are produced by protons injected more recently. We suggest that the blast wave formed in a tidal disruption event (TDE) caused by the supermassive black hole (Sgr A*) could serve as such a fading accelerator. With typical parameters of the TDE blast wave, gamma-ray spectra of both the CMZ region and HESS J1745-290 can be reproduced simultaneously. Meanwhile, we find that the cosmic-ray energy density profile in the CMZ region may also be reproduced in the fading accelerator model when appropriate combinations of the particle injection history and the diffusion coefficient of cosmic rays are adopted.

  10. 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.

  11. 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

  12. 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.

  13. 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

    2013-12-02

    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.

  14. 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.

  15. Performance evaluation and channel modeling of MIMO free space optical communication system

    NASA Astrophysics Data System (ADS)

    Deng, Tianping; Lu, Yimin; Lu, Gang; Peng, Kai

    2005-11-01

    Free space optical communication systems represent one of the most promising approaches for addressing the emerging broadband access market, it can provide high bandwidth with no physical contact, but are hampered by signal fading effects due to particulate scattering caused by atmospheric turbulence. In this paper, we propose a new channel model of MIMO free space optical communication system. The physics meaning of this model is very clear, and its format is very simple. Mathematic results show that MIMO is a very effective way for intensity fluctuation reduction induced by turbulence, thus reduce the bit-error-rate of the system.

  16. 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.

  17. A comparison of CIE L*a*b* and spectral methods for the analysis of fading in sliced cured ham

    NASA Astrophysics Data System (ADS)

    Sheridan, C.; O'Farrell, M.; Lewis, E.; Flanagan, C.; Kerry, J.; Jackman, N.

    2007-06-01

    In the modern retail environment, the appearance of a product is frequently the only quality indicator available to consumers. This is especially true of products such as sliced ham that have been sealed into packages to maintain product freshness. It has been shown that sliced ham products undergo discolouration from their original pink colour to a pale grey colour when exposed to a combination of oxygen and light. This is unappealing to consumers who expect a pink colour for sliced ham. An investigation is made into a sensor that would monitor the initial colour status of cured ham before packaging in order to determine the amount of time left before the ham fades to an unsatisfactory colour. For this sensor to operate, appropriate analysis of the appearance of the meat is required. Two methods for the measurement of the fading were investigated—CIE L*a*b* measurements and analysis of the spectral reflectance of the colour of the ham. Several sliced ham products with differing amounts of fading were examined using both methods. It was observed that the products used covered a wide range of variation in colour. Reproducibility of CIE L*a*b* values proved to be quite difficult and significant overlapping of the L* (lightness) and a* (redness) values measured for pink and grey coloured ham was observed. The variations in these values can be attributed to differences in the intensity of reflected light for different products. L*a*b* measurements are sensitive to light intensity and pigment concentration. Analysis of the spectral reflectance readings did not encounter these problems as the spectral response was normalized (to reduce intensity errors) before data analysis was carried out on the spectral shape or 'pattern' using principal component analysis (PCA) and artificial neural networks (ANN). A classifier based on PCA and ANN was successfully implemented that can discriminate different stages of fading for the ham slices. A case study was carried out on ham

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. An Introduction to Backwards Faded Scaffolding in the ASTRO 101 Laboratory Course

    NASA Astrophysics Data System (ADS)

    Slater, S. J.; Slater, T. F.; Lyons, D. J.; Sibbernsen, K.; Robison, P.

    2011-09-01

    The Boyer Report, "Reinventing Undergraduate Education," eloquently argues that all undergraduate coursework would benefit greatly by being framed as authentic research experiences where students create and defend knowledge. Yet, our experience in guiding students to do research projects using astronomical databases has demonstrated time and time again that the most difficult aspect of engaging in scientific research is helping students identify and frame a fruitful research question itself. To scaffold students' learning experiences to help them ask better research questions, we have adopted a backwards faded scaffolding approach where students do multiple inquiry experiences, rather than a single protracted one. In this approach, we first carefully guide students through an entire astronomical inquiry sequence, from giving them the targeted research question through an accurate scientific conclusion tightly matched to the research question. Then, for their second inquiry experience, students generate their conclusions independently, with the previous experience set out as a guide. Students are required to make sense of data that has been purposefully planned, collected, and analyzed with instructor guidance. They construct and defend conclusions based upon data that is, effectively, given to them. By the time students reach their third inquiry, they have been exposed to two experiences in which they were guided through. During this third inquiry, data collection and analysis become independent tasks. By the fourth inquiry, students have received explicit instruction on the connection between the research questions and the procedure undertaken to address them three times. They are prepared to take responsibility for creating a plausible method for collecting data given a research prompt. By the fifth inquiry, students have now seen four examples of quality research questions/hypotheses and their relationship to procedures, data collection, and conclusions. At this

  6. 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.

  7. Mitigating voltage and capacity fading of lithium-rich layered cathodes by lanthanum doping

    NASA Astrophysics Data System (ADS)

    Yu, Ruizhi; Wang, Gang; Liu, Meihong; Zhang, Xiaohui; Wang, Xianyou; Shu, Hongbo; Yang, Xiukang; Huang, Weihua

    2016-12-01

    La-doped lithium-rich layered oxide material Li1.2Mn0.54-xNi0.13Co0.13LaxO2 (x = 0.01, 0.02, 0.03) is firstly synthesized via a solvothermal method and subsequent high-temperature calcination technique. The effects of La substitution for partial Mn on the structure and electrochemical performance of materials are systematically studied by inductively coupled plasma optical emission spectroscopy (ICP-OES), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscope (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and electrochemical measurement. The results reveal that La is effectively and homogenously doped into the materials, which can expand pathway for intercalation/deintercalation of Li+ ions. In addition, owing to La doping, the Li1.2Mn0.52Ni0.13Co0.13La0.02O2 sample exhibits 93.2% capacity retention after 100 cycles at 1 C. More importantly, this doping can effectively restrain the decrease of average discharge voltage upon cycling, which is one of the longstanding fatal drawbacks for lithium-rich layered oxide material. Moreover, La doping can stabilize the layered framework upon long term cycling and suppress voltage fading, and thus resulting in the better cycling performance. Additionally, the rate capability is also improved by La doping due to the higher diffusion velocity of Li+ ions.

  8. Correlation of Arrhenius behaviors in power and capacity fades with cell impedance and heat generation in cylindrical lithium-ion cells

    NASA Astrophysics Data System (ADS)

    Liaw, Bor Yann; Roth, E. Peter; Jungst, Rudolph G.; Nagasubramanian, Ganesan; Case, Herbert L.; Doughty, Daniel H.

    A series of cylindrical 18650 lithium-ion cells with an MAG-10|1.2 M LiPF 6 ethylene carbonate (EC):ethyl methyl carbonate (EMC) (w:w=3:7)|Li xNi 0.8Co 0.15Al 0.05O 2 configuration were made and tested for power-assist hybrid electric vehicle (HEV) applications under various aging conditions of temperature and state-of-charge (SOC). The cells were intermittently characterized for changes in power capability, rate capacity, and impedance as aging progressed. The changes of these properties with temperature, as depicted by Arrhenius equations, were analyzed. We found that the degradation in power and capacity fade seems to relate to the impedance increase in the cell. The degradation follows a multi-stage process. The initial stage of degradation has an activation energy of the order of 50-55 kJ/mol, as derived from power fade and C1 capacity fade measured at C/1 rate. In addition, microcalorimetry was performed on two separate unaged cells at 80% SOC at various temperatures to measure static heat generation in the cells. We found that the static heat generation has an activation energy of the order of 48-55 kJ/mol, similar to those derived from power and C1 capacity fade. The correspondence in the magnitude of the activation energy suggests that the power and C1 capacity fades were related to the changes of the impedance in the cells, most likely via the same fading mechanism. The fading mechanism seemed to be related to the static heat generation of the cell.

  9. Quasi-Anonymous Channels

    DTIC Science & Technology

    2003-01-01

    QUASI- ANONYMOUS CHANNELS Ira S. Moskowitz Center for High Assurance Computer Systems - Code 5540 Naval Research Laboratory, Washington, DC...Assurance Computer Systems - Code 5540 Naval Research Laboratory, Washington, DC 20375, USA Abstract Although both anonymity and covert...channels are part of the larger topic of information hiding, there also exists an intrinsic linkage between anonymity and covert channels. This linkage

  10. Interleaved convolutional coding for the turbulent atmospheric optical communication channel

    NASA Astrophysics Data System (ADS)

    Davidson, Frederic M.; Koh, Yutai T.

    1988-09-01

    The coding gain of a constraint-length-three, rate one-half convolutional code over a long clear-air atmospheric direct-detection optical communication channel using binary pulse-position modulation signaling was directly measured as a function of interleaving delay for both hard- and soft-decision Viterbi decoding. Maximum coding gains theoretically possible for this code with perfect interleaving and physically unrealizable perfect-measurement decoding were about 7 dB under conditions of weak clear-air turbulence, and 11 dB at moderate turbulence levels. The time scale of the fading (memory) of the channel was directly measured to be tens to hundreds of milliseconds, depending on turbulence levels. Interleaving delays of 5 ms between transmission of the first and second channel bits output by the encoder yield coding gains within 1.5 dB of theoretical limits with soft-decision Viterbi decoding. Coding gains of 4-5 dB were observed with only 100 microseconds of interleaving delay. Soft-decision Viterbi decoding always yielded 1-2 dB more coding gain than hard-decision Viterbi decoding.

  11. Channel modelling for free-space optical inter-HAP links using adaptive ARQ transmission

    NASA Astrophysics Data System (ADS)

    Parthasarathy, S.; Giggenbach, D.; Kirstädter, A.

    2014-10-01

    Free-space optical (FSO) communication systems have seen significant developments in recent years due to growing need for very high data rates and tap-proof communication. The operation of an FSO link is suited to diverse variety of applications such as satellites, High Altitude Platforms (HAPs), Unmanned Aerial Vehicles (UAVs), aircrafts, ground stations and other areas involving both civil and military situations. FSO communication systems face challenges due to different effects of the atmospheric channel. FSO channel primarily suffers from scintillation effects due to Index of Refraction Turbulence (IRT). In addition, acquisition and pointing becomes more difficult because of the high directivity of the transmitted beam: Miss-pointing of the transmitted beam and tracking errors at the receiver generate additional fading of the optical signal. High Altitude Platforms (HAPs) are quasi-stationary vehicles operating in the stratosphere. The slowly varying but precisely determined time-of-flight of the Inter-HAP channel adds to its characteristics. To propose a suitable ARQ scheme, proper theoretical understanding of the optical atmospheric propagation and modeling of a specific scenario FSO channel is required. In this paper, a bi-directional symmetrical Inter-HAP link has been selected and modeled. The Inter-HAP channel model is then investigated via simulations in terms of optical scintillation induced by IRT and in presence of pointing error. The performance characteristic of the model is then quantified in terms of fading statistics from which the Packet Error Probability (PEP) is calculated. Based on the PEP characteristics, we propose suitable ARQ schemes.

  12. 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

  13. 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

  14. Incompatibility of quantum channels

    NASA Astrophysics Data System (ADS)

    Heinosaari, Teiko; Miyadera, Takayuki

    2017-03-01

    Two quantum channels are called compatible if they can be obtained as marginals from a single broadcasting channel; otherwise they are incompatible. We derive a characterization of the compatibility relation in terms of concatenation and conjugation, and we show that all pairs of sufficiently noisy quantum channels are compatible. The complement relation of incompatibility can be seen as a unifying aspect for several important quantum features, such as impossibility of universal broadcasting and unavoidable measurement disturbance. We show that the concepts of entanglement breaking channel and antidegradable channel can be completely characterized in terms compatibility.

  15. On 1-qubit channels

    NASA Astrophysics Data System (ADS)

    Uhlmann, Armin

    2001-09-01

    The entropy HT (ρ) of a state with respect to a channel T and the Holevo capacity of the channel require the solution of difficult variational problems. For a class of 1-qubit channels, which contains all the extremal ones, the problem can be significantly simplified by attaching a unique Hermitian antilinear operator ϑ to every channel of the considered class. The channel's concurrence CT can be expressed by ϑ and turns out to be a flat roof. This allows to write down an explicit expression for HT. Its maximum would give the Holevo (one-shot) capacity.

  16. 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.

  17. 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.

  18. 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.

  19. 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

  20. Mechanically Activated Ion Channels.

    PubMed

    Ranade, Sanjeev S; Syeda, Ruhma; Patapoutian, Ardem

    2015-09-23

    Mechanotransduction, the conversion of physical forces into biochemical signals, is essential for various physiological processes such as the conscious sensations of touch and hearing, and the unconscious sensation of blood flow. 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.

  1. 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

  2. Proceedings of Seminar on Frequency Selective Fading and Its Effect on Digital LOS Radio. Report Number 2.

    DTIC Science & Technology

    1980-01-01

    A0-A087 793 DEFENSE COMMUNICATIONS EN6INEERING CENTER RESTON VA F /G 17/2.1 PROCEEDIN’S OF SEMINAR ON FREQUENCY SELECTIVE FADING AND ITS EF--ETC(U)UN...technical inquiries concerning this document are welcome, and should be directed to: Director Defense Communications Engineering Center D T f ’: 1860...J L Ii C-) 0% 0.. Lii -D E 0H= F - - - o un C,, Lai U. V)~~~ Li CW~ Lmi *L CC Ln- Ci (D _,, .1- k71-3 mt LUJCl I- - L . J r-4 V) -j F L 0- Q CL V) mJ

  3. 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

  4. Quadrature Amplitude Modulation Division for Multiuser MISO Broadcast Channels

    NASA Astrophysics Data System (ADS)

    Dong, Zheng; Zhang, Yan-Yu; Zhang, Jian-Kang; Gao, Xiang-Chuan

    2016-12-01

    This paper considers a discrete-time multiuser multiple-input single-output (MISO) Gaussian broadcast channel~(BC), in which channel state information (CSI) is available at both the transmitter and the receivers. The flexible and explicit design of a uniquely decomposable constellation group (UDCG) is provided based on pulse amplitude modulation (PAM) and rectangular quadrature amplitude modulation (QAM) constellations. With this, a modulation division (MD) transmission scheme is developed for the MISO BC. The proposed MD scheme enables each receiver to uniquely and efficiently detect their desired signals from the superposition of mutually interfering cochannel signals in the absence of noise. In our design, the optimal transmitter beamforming problem is solved in a closed-form for two-user MISO BC using max-min fairness as a design criterion. Then, for a general case with more than two receivers, we develop a user-grouping-based beamforming scheme, where the grouping method, beamforming vector design and power allocation problems are addressed by using weighted max-min fairness. It is shown that our proposed approach has a lower probability of error compared with the zero-forcing (ZF) method when the Hermitian angle between the two channel vectors is small in a two-user case. In addition, simulation results also reveal that for the general channel model with more than two users, our user-grouping-based scheme significantly outperforms the ZF, time division (TD), minimum mean-square error (MMSE) and signal-to-leakage-and-noise ratio (SLNR) based techniques in moderate and high SNR regimes when the number of users approaches to the number of base station (BS) antennas and it degrades into the ZF scheme when the number of users is far less than the number of BS antennas in Rayleigh fading channels.

  5. Baseband pulse shaping for pi /4 FQPSK in nonlinearly amplified mobile channels

    NASA Astrophysics Data System (ADS)

    Subasinghe-Dias, Dileeka; Feher, Kamilo

    1994-10-01

    We apply baseband pulse shaping techniques for pi /4 QPSK in order to reduce the spectral regeneration of the bandlimited carrier after nonlinear amplification. These Feher's patented techniques, namely, pi /4 FQPSK (superposed QPSK) and pi /4 CTPSK (controlled transition PSK), may also be noncoherently demodulated. Application of these techniques is in fast fading, power efficient channels, typical of the mobile radio environment. Patents related to FQPSK are described. Computer simulation and experimental studies demonstrate that with these baseband waveshaping techniques, carrier envelope fluctuations are significantly reduced, and the out-of-band power after nonlinear amplification is suppressed by up to 20 dB compared to pi /4 QPSK. In frequency noninterleaved land or satellite mobile radio systems operating in a nonlinear, fading and ACI (adjacent channel interference) environment, these techniques may achieve 20%-50% higher spectral efficiency compared to pi /4 QPSK. In mobile cellular systems using pi /4 QPSK, such as the new North American and the Japanese digital cellular systems, the application of these baseband pulse shapes may allow more convenient and less costly amplifier linearization.

  6. Cholesterol and Kir channels

    PubMed Central

    Levitan, Irena

    2009-01-01

    To date, most of the major types of Kir channels, Kir2s, Kir3s, Kir4s and Kir6s, have been found to partition into cholesterol-rich membrane domains and/or to be regulated by changes in the level of membrane cholesterol. Surprisingly, however, in spite of the structural similarities between different Kirs, effects of cholesterol on different types of Kir channels vary from cholesterol-induced decrease in the current density (Kir2 channels) to the loss of channel activity by cholesterol depletion (Kir4 channels) and loss of channel coupling by different mediators (Kir3 and Kir6 channels). Recently, we have gained initial insights into the mechanisms responsible for cholesterol-induced suppression Kir2 channels, but mechanisms underlying cholesterol sensitivity of other Kir channels are mostly unknown. The goal of this review is to present a summary of the current knowledge of the distinct effects of cholesterol on different types of Kir channels in vitro and in vivo. PMID:19548316

  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

    2016-09-08

    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.

  9. Joint source-channel coding for wireless object-based video communications utilizing data hiding.

    PubMed

    Wang, Haohong; Tsaftaris, Sotirios A; Katsaggelos, Aggelos K

    2006-08-01

    In recent years, joint source-channel coding for multimedia communications has gained increased popularity. However, very limited work has been conducted to address the problem of joint source-channel coding for object-based video. In this paper, we propose a data hiding scheme that improves the error resilience of object-based video by adaptively embedding the shape and motion information into the texture data. Within a rate-distortion theoretical framework, the source coding, channel coding, data embedding, and decoder error concealment are jointly optimized based on knowledge of the transmission channel conditions. Our goal is to achieve the best video quality as expressed by the minimum total expected distortion. The optimization problem is solved using Lagrangian relaxation and dynamic programming. The performance of the proposed scheme is tested using simulations of a Rayleigh-fading wireless channel, and the algorithm is implemented based on the MPEG-4 verification model. Experimental results indicate that the proposed hybrid source-channel coding scheme significantly outperforms methods without data hiding or unequal error protection.

  10. 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.

  11. Cramer-Rao Lower Bound Evaluation for Linear Frequency Modulation Based Active Radar Networks Operating in a Rice Fading Environment

    PubMed Central

    Shi, Chenguang; Salous, Sana; Wang, Fei; Zhou, Jianjiang

    2016-01-01

    This paper investigates the joint target parameter (delay and Doppler) estimation performance of linear frequency modulation (LFM)-based radar networks in a Rice fading environment. The active radar networks are composed of multiple radar transmitters and multichannel receivers placed on moving platforms. First, the log-likelihood function of the received signal for a Rician target is derived, where the received signal scattered off the target comprises of dominant scatterer (DS) component and weak isotropic scatterers (WIS) components. Then, the analytically closed-form expressions of the Cramer-Rao lower bounds (CRLBs) on the Cartesian coordinates of target position and velocity are calculated, which can be adopted as a performance metric to access the target parameter estimation accuracy for LFM-based radar network systems in a Rice fading environment. It is found that the cumulative Fisher information matrix (FIM) is a linear combination of both DS component and WIS components, and it also demonstrates that the joint CRLB is a function of signal-to-noise ratio (SNR), target’s radar cross section (RCS) and transmitted waveform parameters, as well as the relative geometry between the target and the radar network architectures. Finally, numerical results are provided to indicate that the joint target parameter estimation performance of active radar networks can be significantly improved with the exploitation of DS component. PMID:27929433

  12. In-situ X-ray absorption spectroscopy analysis of capacity fade in nanoscale-LiCoO2

    NASA Astrophysics Data System (ADS)

    Patridge, Christopher J.; Love, Corey T.; Swider-Lyons, Karen E.; Twigg, Mark E.; Ramaker, David E.

    2013-07-01

    The local structure of nanoscale (∼10-40 nm) LiCoO2 is monitored during electrochemical cycling utilizing in-situ X-ray absorption spectroscopy (XAS). The high surface area of the LiCoO2 nanoparticles not only enhances capacity fade, but also provides a large signal from the particle surface relative to the bulk. Changes in the nanoscale LiCoO2 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 LiCoO2 as a likely factor in the capacity fade and irreversible losses in practical, microscale LiCoO2.

  13. FODA/IBEA-TDMA - A flexible fade countermeasure system for integrated services in user-oriented networks

    NASA Astrophysics Data System (ADS)

    Celandroni, N.; Ferro, E.; James, N.; Potorti, F.

    1992-12-01

    A flexible, processor based, TDMA station has been implemented. This station and its associated variable data rate modem enables users to implement very complex frame structures under software control. Burst rates of 512 kb/s-8x192 Mb/s and different coding rates are possible allowing the transmitted bit energy from each station in the network to be adapted to prevailing conditions. The proposed application of the station is the transmission of mixed stream and packet traffic, in a LANs interconnection via satellite environment, using a modification of the FODA technique. The association of the up-link power control feature with the bit and coding rate variation gives the system an interesting ability to cope with fade conditions. The link outage probability is investigated for the Olympus transponder in Ka band. The ability of the system, together with the good performance of Olympus, shows that the Ka band is usable for the above mentioned types of networks without prohibitive fade degradation, at least for limited coverages.

  14. Cramer-Rao Lower Bound Evaluation for Linear Frequency Modulation Based Active Radar Networks Operating in a Rice Fading Environment.

    PubMed

    Shi, Chenguang; Salous, Sana; Wang, Fei; Zhou, Jianjiang

    2016-12-06

    This paper investigates the joint target parameter (delay and Doppler) estimation performance of linear frequency modulation (LFM)-based radar networks in a Rice fading environment. The active radar networks are composed of multiple radar transmitters and multichannel receivers placed on moving platforms. First, the log-likelihood function of the received signal for a Rician target is derived, where the received signal scattered off the target comprises of dominant scatterer (DS) component and weak isotropic scatterers (WIS) components. Then, the analytically closed-form expressions of the Cramer-Rao lower bounds (CRLBs) on the Cartesian coordinates of target position and velocity are calculated, which can be adopted as a performance metric to access the target parameter estimation accuracy for LFM-based radar network systems in a Rice fading environment. It is found that the cumulative Fisher information matrix (FIM) is a linear combination of both DS component and WIS components, and it also demonstrates that the joint CRLB is a function of signal-to-noise ratio (SNR), target's radar cross section (RCS) and transmitted waveform parameters, as well as the relative geometry between the target and the radar network architectures. Finally, numerical results are provided to indicate that the joint target parameter estimation performance of active radar networks can be significantly improved with the exploitation of DS component.

  15. 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.

  16. R type anion channel

    PubMed Central

    Diatloff, Eugene; Peyronnet, Rémi; Colcombet, Jean; Thomine, Sébastien; Barbier-Brygoo, Hélène

    2010-01-01

    Plant genomes code for channels involved in the transport of cations, anions and uncharged molecules through membranes. Although the molecular identity of channels for cations and uncharged molecules has progressed rapidly in the recent years, the molecular identity of anion channels has lagged behind. Electrophysiological studies have identified S-type (slow) and R-type (rapid) anion channels. In this brief review, we summarize the proposed functions of the R-type anion channels which, like the S-type, were first characterized by electrophysiology over 20 years ago, but unlike the S-type, have still yet to be cloned. We show that the R-type channel can play multiple roles. PMID:21051946

  17. 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.

  18. Switchable topological phonon channels

    NASA Astrophysics Data System (ADS)

    Süsstrunk, Roman; Zimmermann, Philipp; Huber, Sebastian D.

    2017-01-01

    Guiding energy deliberately is one of the central elements in engineering and information processing. It is often achieved by designing specific transport channels in a suitable material. Topological metamaterials offer a way to construct stable and efficient channels of unprecedented versatility. However, due to their stability it can be tricky to terminate them or to temporarily shut them off without changing the material properties massively. While a lot of effort was put into realizing mechanical topological metamaterials, almost no works deal with manipulating their edge channels in sight of applications. Here, we take a step in this direction, by taking advantage of local symmetry breaking potentials to build a switchable topological phonon channel.

  19. Selfcomplementary Quantum Channels

    NASA Astrophysics Data System (ADS)

    Smaczyński, Marek; Roga, Wojciech; Życzkowski, Karol

    2016-10-01

    Selfcomplementary quantum channels are characterized by such an interaction between the principal quantum system and the environment that leads to the same output states of both interacting systems. These maps can describe approximate quantum copy machines, as perfect copying of an unknown quantum state is not possible due to the celebrated no-cloning theorem. We provide here a parametrization of a large class of selfcomplementary channels and analyze their properties. Selfcomplementary channels preserve some residual coherences and residual entanglement. Investigating some measures of non-Markovianity, we show that time evolution under selfcomplementary channels is highly non-Markovian.

  20. Ion channels in asthma.

    PubMed

    Valverde, Miguel A; Cantero-Recasens, Gerard; Garcia-Elias, Anna; Jung, Carole; Carreras-Sureda, Amado; Vicente, Rubén

    2011-09-23

    Ion channels are specialized transmembrane proteins that permit the passive flow of ions following their electrochemical gradients. In the airways, ion channels participate in the production of epithelium-based hydroelectrolytic secretions and in the control of intracellular Ca(2+) levels that will ultimately activate almost all lung cells, either resident or circulating. Thus, ion channels have been the center of many studies aiming to understand asthma pathophysiological mechanisms or to identify therapeutic targets for better control of the disease. In this minireview, we focus on molecular, genetic, and animal model studies associating ion channels with asthma.

  1. An iterative detection method of MIMO over spatial correlated frequency selective channel: using list sphere decoding for simplification

    NASA Astrophysics Data System (ADS)

    Shi, Zhiping; Yan, Bing

    2010-08-01

    In multiple-input multiple-output(MIMO) wireless systems, combining good channel codes(e.g., Non-binary Repeat Accumulate codes) with adaptive turbo equalization is a good option to get better performance and lower complexity under Spatial Correlated Frequency Selective(SCFS) Channel. The key of this method is after joint antennas MMSE detection (JAD/MMSE) based on interruption cancelling using soft information, considering the detection result as an output of a Gaussian equivalent flat fading channel, and performing maximum likelihood detection(ML) to get more correct estimated result. But the using of ML brings great complexity increase, which is not allowed. In this paper, a low complexity method called list sphere decoding is introduced and applied to replace the ML in order to simplify the adaptive iterative turbo equalization system.

  2. Design and evaluation of an IDM-based MIMO FSO system over Gamma-Gamma turbulence channels

    NASA Astrophysics Data System (ADS)

    Zhang, Chenglei; Zhou, Xiaolin; Zheng, Xiaowei; Du, Jianhong

    2011-12-01

    In this paper, we design an interleave-division-multiplexing (IDM) based multiple-input multiple-output (MIMO) free-space optics (FSO) communication system. The system overcomes problems harassing conventional optical MIMO systems such as restrictions of antenna number and high complexity in receiver. An iterative on-off keying (OOK) modulated IDM MIMO detection algorithm is developed. Expression of an upper bound of frame-error-rate (FER) is derived. In addition, we evaluate the BER performance of the proposed optical MIMO scheme in various FSO scenarios. Simulations confirm that the proposed scheme can effectively increase the feasibility of FSO communications over Gamma-Gamma turbulence-induced fading channels.

  3. 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.

  4. Ion channels in toxicology.

    PubMed

    Restrepo-Angulo, Iván; De Vizcaya-Ruiz, Andrea; Camacho, Javier

    2010-08-01

    Ion channels play essential roles in human physiology and toxicology. Cardiac contraction, neural transmission, temperature sensing, insulin release, regulation of apoptosis, cellular pH and oxidative stress, as well as detection of active compounds from chilli, are some of the processes in which ion channels have an important role. Regulation of ion channels by several chemicals including those found in air, water and soil represents an interesting potential link between environmental pollution and human diseases; for instance, de novo expression of ion channels in response to exposure to carcinogens is being considered as a potential tool for cancer diagnosis and therapy. Non-specific binding of several drugs to ion channels is responsible for a huge number of undesirable side-effects, and testing guidelines for several drugs now require ion channel screening for pharmaceutical safety. Animal toxins targeting human ion channels have serious effects on the population and have also provided a remarkable tool to study the molecular structure and function of ion channels. In this review, we will summarize the participation of ion channels in biological processes extensively used in toxicological studies, including cardiac function, apoptosis and cell proliferation. Major findings on the adverse effects of drugs on ion channels as well as the regulation of these proteins by different chemicals, including some pesticides, are also reviewed. Association of ion channels and toxicology in several biological processes strongly suggests these proteins to be excellent candidates to follow the toxic effects of xenobiotics, and as potential early indicators of life-threatening situations including chronic degenerative diseases.

  5. 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

  6. 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

  7. 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.

  8. The channels of Mars

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1982-01-01

    Early observations of Mars conducted by means of telescopes are considered. Secchi introduced the Italian word 'canale' ('channel') in 1869 to describe apparent lines on the planet's surface. Between 1877 and 1888 Schiaparelli mapped a profusion of 'canali'. Schiaparelli's work led to famous controversies about Mars. This book attempts to investigate the puzzle posed by the Martian channels, taking into account also the results of the studies conducted with the aid of the two orbiting Viking spacecraft which have produced a total number of nearly 60,000 pictures. The channel types are discussed along with questions regarding the distribution, the ages, and the proposed origins of the channels. Attention is given to the geomorphology of Mars, the patterns and networks of Martian valleys, ice and the Martian surface, the outflow channels, catastrophic flood processes, questions of analogy between terrestrial and Martian geographic features, and Martian phenomena associated with water liquid or water ice.

  9. Performance of a Spectrally Encoded Multi-Carrier Phase Shift Keying Communications System in a Frequency-Selective, Slowly-Fading Multipath Channel

    DTIC Science & Technology

    2005-03-01

    Wright-Patterson AFB OH, March 2004. AFIT/GE/ENG/04-20. 7. Papoulis, Athanasios and S. Unnikrishna Pillai . Probability, Random Variables, and...Upper Saddle River, New Jersey 07458, 2001. 129 13. Swackhammer, Patrick J. Design and Simulation of a Multiple Access Trans- form Domain Communication

  10. Performance Analysis of Cooperative ARQ Scheme with Co-channel Interference

    NASA Astrophysics Data System (ADS)

    Zhang, Tao; Cheng, Yunpeng; Cai, Yueming; Yang, Weiwei; Chen, Hualiang

    2013-12-01

    In this paper, the performance of cooperative decode-and-forward (DF) automatic-repeat-request (ARQ) scheme with co-channel interference is investigated in a long-term static Rayleigh fading environment. We assume that the relay node is impaired by M interferers and the destination node is impaired by N interferers. A closed-form expression for the outage probability of cooperative DF ARQ scheme with co-channel interference is derived. Then we analyze the average throughput of the scheme with co-channel interference and further derive that the average throughput is mainly influenced by the interferers at the destination node. The average total power consumption per information packet of cooperative DF ARQ scheme with co-channel interference is investigated and a closed-form expression is obtained for cooperative DF ARQ scheme with co-channel interference, in which the source and relay may use different transmission power level in different transmission time slots. The closed-form expression is valid for any maximum number of transmission time slots L allowed by the protocol and may play a key role in optimizing power allocation. Numerical and simulation results are presented to verify our analysis.

  11. Suppressing the voltage-fading of layered lithium-rich cathode materials via an aqueous binder for Li-ion batteries.

    PubMed

    Zhang, Tao; Li, Jun-tao; Liu, Jie; Deng, Ya-ping; Wu, Zhen-guo; Yin, Zu-wei; Guo, Dong; Huang, Ling; Sun, Shi-gang

    2016-03-28

    Guar gum (GG) has been applied as a binder for layered lithium-rich cathode materials of Li-ion batteries for the first time. Compared with the conventional PVDF binder, electrodes with GG as the binder exhibit significantly suppressed voltage and capacity fading. This study has introduced a multi-functional binder for layered lithium-rich cathode materials.

  12. 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.

  13. 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.

  14. Manipulation of Motivating Operations and Use of a Script-Fading Procedure to Teach Mands for Location to Children with Language Delays

    ERIC Educational Resources Information Center

    Howlett, Melissa A.; Sidener, Tina M.; Progar, Patrick R.; Sidener, David W.

    2011-01-01

    The effects of contriving motivating operations (MOs) and script fading on the acquisition of the mand "Where's [object]?" were evaluated in 2 boys with language delays. During each session, trials were alternated in which high-preference items were present (abolishing operation [AO] trials) or missing (establishing operation [EO] trials) from…

  15. Assay for calcium channels

    SciTech Connect

    Glossmann, H.; Ferry, D.R.

    1985-01-01

    This chapter focuses on biochemical assays for Ca/sup 2 +/-selective channels in electrically excitable membranes which are blocked in electrophysiological and pharmacological experiments by verapamil, 1,4-dihydropyridines, diltiazen (and various other drugs), as well as inorganic di- or trivalent cations. The strategy employed is to use radiolabeled 1,4-dihydropyridine derivatives which block calcium channels with ED/sub 50/ values in the nanomolar range. Although tritiated d-cis-diltiazem and verapamil can be used to label calcium channels, the 1,4-dihydropyridines offer numerous advantages. The various sections cover tissue specificity of channel labeling, the complex interactions of divalent cations with the (/sup 3/H)nimodipine-labeled calcium channels, and the allosteric regulation of (/sup 3/H)nimodipine binding by the optically pure enantiomers of phenylalkylamine and benzothiazepine calcium channel blockers. A comparison of the properties of different tritiated 1,4-dihydropyridine radioligands and the iodinated channel probe (/sup 125/I)iodipine is given.

  16. 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.

  17. 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.

  18. 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.

  19. Fractional channel multichannel analyzer

    DOEpatents

    Brackenbush, L.W.; Anderson, G.A.

    1994-08-23

    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 asynchronous 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. 9 figs.

  20. 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.