Embolic Doppler ultrasound signal detection using discrete wavelet transform

Asymptomatic circulating emboli can be detected by Doppler ultrasound. Embolic Doppler ultrasound signals are short duration transient like signals. The wavelet transform is an ideal method for analysis and detection of such signals by optimizing time-frequency resolution. We propose a detection system based on the discrete wavelet transform (DWT) and study some parameters, which might be useful for describing embolic signals (ES). We used a fast DWT algorithm based on the Daubechies eighth-order wavelet filters with eight scales. In order to evaluate feasibility of the DWT of ES, two independent data sets, each comprising of short segments containing an ES (N=100), artifact (N=100) or Doppler speckle (DS) (N=100), were used. After applying the DWT to the data, several parameters were evaluated. The threshold values used for both data sets were optimized using the first data set. While the DWT coefficients resulting from artifacts dominantly appear at the higher scales (five, six, seven, and eight), the DWT coefficients at the lower scales (one, two, three, and four) are mainly dominated by ES and DS. The DWT is able to filter out most of the artifacts inherently during the transform process. For the first data set, 98 out of 100 ES were detected as ES. For the second data set, 95 out of 100 ES were detected as ES when the same threshold values were used. The algorithm was also tested with a third data set comprising 202 normal ES; 198 signals were detected as ES.     

A cusum change-point detection algorithm for non-stationary sequences with application to data network surveillance

We adapt the classic cusum change-point detection algorithm to handle non-stationary sequences that are typical with network surveillance applications. The proposed algorithm uses a defined timeslot structure to take into account time varying distributions, and uses historical samples of observations within each timeslot to facilitate a nonparametric methodology. Our proposed solution includes an on-line screening feature that fully automates the implementation of the algorithm and eliminates the need for manual oversight up until the point where root cause analysis begins.     

Bounds on the Sum Capacity of Synchronous Binary CDMA Channels

In this paper, we obtain a family of lower bounds for the sum capacity of code-division multiple-access (CDMA) channels assuming binary inputs and binary signature codes in the presence of additive noise with an arbitrary distribution. The envelope of this family gives a relatively tight lower bound in terms of the number of users, spreading gain, and the noise distribution. The derivation methods for the noiseless and the noisy channels are different but when the noise variance goes to zero, the noisy channel bound approaches the noiseless case. The behavior of the lower bound shows that for small noise power, the number of users can be much more than the spreading gain without any significant loss of information (overloaded CDMA). A conjectured upper bound is also derived under the usual assumption that the users send out equally likely binary bits in the presence of additive noise with an arbitrary distribution. As the noise level increases, and/or, the ratio of the number of users and the spreading gain increases, the conjectured upper bound approaches the lower bound. We have also derived asymptotic limits of our bounds that can be compared to a formula that Tanaka obtained using techniques from statistical physics; his bound is close to that of our conjectured upper bound for large scale systems.     

Efficient rank-ordered mean (ROM) techniques for the recovery ofisolated losses in highly corrupted images

This paper proposes two efficient rank-ordered mean (ROM)-based techniques to conceal isolated losses in any image. The first technique is an iterative ROM-based technique while the second one is a modified version of ROM filtering. Both techniques have better performances than the SD-ROM technique especially for high loss percentages     

A Note on "Modulation Methods Related to Sine Wave Crossings"

In this correspondence we show that the above paper is a rediscovery of what was known since 1973 [1]. The contents of the paper have been published in various forms in the literature. The more general case of a periodic wave crossing has already been considered, which covers the special case of a sine wave crossing.     

Robust Audio Data Hiding Using Correlated Quantization With Histogram-Based Detector

In this paper, two blind audio watermarking methods using correlated quantization for data embedding with histogram-based detector have been proposed. First, a novel mapping called the point-to-point graph (PPG) is introduced. In this mapping, the value of samples is important as well as the correlation among them. As this mapping increases the dimension of the signal, the data embedding procedure (quantization) will be diversified more securely than that of the 1-D domains such as the time or frequency domains. Hence, two watermarking techniques coined as hard and soft quantization methods based on the quantization of the PPG point radii are suggested. The performance of both techniques is analyzed by obtaining the radii distribution of PPG points after watermarking. Experimental results against AWGN attack confirm the validity of theoretical analysis. Moreover, the robustness of the proposed methods against other common attacks such as echo, low pass, resampling, and MP3 are investigated through extensive simulations.     

Effect of rare earth element additions on the impression creep of Sn–9Zn solder alloy

Creep behavior of the Sn–9Zn–RE alloys containing 0.1, 0.25 and 0.5 wt.% rare earth (RE) elements was studied by impression testing and compared to that of the eutectic Sn–9Zn alloy. The tests were carried out under constant punching stress in the range 40–135 MPa and at temperatures in the range 298–420 K. Results showed that for all loads and temperatures, Sn–9Zn–0.25RE had the lowest creep rate, and thus the highest creep resistance among all materials tested. This was attributed to the formation of Sn–RE second phase precipitates which act as the main strengthening agent in the RE-containing Sn–Zn alloys. RE contents higher than 0.25 wt.%, resulted in a lower creep resistance due to a reduction in the volume fraction of Zn-rich phase caused by the formation of Sn–Zn–RE intermetallics. The average stress exponents of 6.8, 6.9, 7.1, 6.8 and activation energies of 42.6, 40.6, 43.0 and 44.9 kJ mol⁻¹ were obtained for Sn–9Zn, Sn–9Zn–0.1RE, Sn–9Zn–0.25RE, and Sn–9Zn–0.5RE, respectively. These activation energies were close to 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about seven suggests that the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion.     

Interpolation of 2-D signals from their isolated zeros

In this paper, interpolation formulas are derived for the recovery of a two-dimensional (2-D) bandlimited signal from its isolated zeros. Different constellations of zero locations are considered. The interpolation formulas, based on Lagrange interpolation, are given both in Cartesian and in polar coordinates.     

Recovery of signals from nonuniform samples using iterative methods

An iterative method to recover a bandlimited signal from its ideal nonuniform samples is proposed. The convergence of iterations is proved, and general regions for convergence are found. It is shown that the iterative method is also applicable to other forms of nonuniform sampling, i.e. natural sampling and interpolated sampling (such as sample-and-hold signal). Simulation results show that this method works effectively and fairly fast, and the errors after a few iterations are negligible if a particular sufficient condition is satisfied or the sampling rate is higher than the Nyquist rate     

Robust Scaling-Based Image Watermarking Using Maximum-Likelihood Decoder With Optimum Strength Factor

In this paper, a new scaling-based image-adaptive watermarking system has been presented, which exploits human visual model for adapting the watermark data to local properties of the host image. Its improved robustness is due to embedding in the low-frequency wavelet coefficients and optimal control of its strength factor from HVS point of view. Maximum likelihood (ML) decoder is used aided by the channel side information. The performance of the proposed scheme is analytically calculated and verified by simulation. Experimental results confirm the imperceptibility of the proposed method and its higher robustness against attacks compared to alternative watermarking methods in the literature.