Experimental and computational validation of a scaled train tunnel model using modal analysis

Acoustic engineers are faced with the challenge of minimising reverberation time in their designs so as to contribute to the health and well-being of those traveling by train and those on the platforms. Although the problem is easy to identify, it is not as simple to solve. The acoustical environment of a train tunnel is complex, with a variety of noise contributing factors such as train announcements, speech of commuters, ventilation systems, electrical equipment and wheel and rail noise. As a result, there is some difficulty in modeling the complete acoustic environment with computational or acoustic first principles. In this study, an experimental rig was constructed to model the acoustic behavior within a tunnel. The modal properties for the 300 Hz to 1500 Hz range, including resonances and mode shapes were identified and were shown to successfully correspond to theoretical results and a computational model created in COMSOL using Finite Element Analysis.     

Global convergence and mixing parameter selection in thecross-correlation constant modulus algorithm for the multi-userenvironment

Surface topography of the mixed cross-correlation and constant modulus algorithm (CC-CMA) is undertaken to provide a suitable range for the mixing parameter to avoid ill-convergence. Previous work indicated that the mixing parameter k should be chosen to be greater than 4/3, but this result was based upon an assumption of perfect equalisation of previous equaliser outputs. The authors relax this perfect equalisation assumption and obtain a tighter bound for the mixing parameter in the case of a two-user system as well as a multi-user system. In a two-user transmission scheme, they suggest that the value of k should be chosen as 4. It is shown that for a multi-user system the cross-correlation of the soft decision of the previous equaliser output may result in ill-convergence and a hybrid equalisation method, which employs a hard decision on the equaliser output in the cross-correlation term of the CC-CMA algorithm after a start-up period is therefore proposed. Simulation studies are included to support the results     

Adaptive blind retrieval techniques for multiuser DS-CDMA signals

In a multiuser direct sequence code division multiple access system, retrieval of the transmitted signals with a conventional receiver is difficult when there is chip asynchronism, multipath propagation and the associated near-far problem. It is shown that despite these problems, an adaptive linear receiver based on a mixed cross-correlation and constant modulus algorithm has the potential to retrieve all users simultaneously. Moreover, for the assumed transmission model, a necessary condition for global convergence of the proposed algorithm is also provided     

Multi-user interference cancellation technology in the presence of multiple frequency offsets

The performance of multi-user detectors in the presence of multiple frequency offsets under a Rayleigh fading channel environment is analysed, and techniques to estimate and remove multiple frequency offsets (FOs) for successive interference cancellation (SIC) and parallel interference cancellation (PIC) receivers are also proposed. The closed form expressions derived for bit error rate (BER) of SIC and PIC schemes in the presence of multiple FOs have been verified using extensive simulation results. The PIC is shown to be less sensitive to frequency offsets as compared to SIC. It is demonstrated through analytical and simulation results that the proposed frequency offset estimation and correction techniques provide approximately 8 dB gain in the BER performance over conventional SIC and PIC schemes in the presence of multiple frequency offsets     

Improved convergence of fractionally-spaced constant modulusequalisers in presence of noise

The constant modulus algorithm (CMA) applied to a fractionally spaced equaliser, with length and zero constraints on the channel, has been shown to be globally convergent when there is no channel noise. However, in the presence of channel noise, the performance of the CMA can suffer because of the existence of undesired local minima corresponding to different delays. A new technique is introduced, based on the Gram-Schmidt orthogonalisation, to obtain convergence to an optimum delay where the mean square error is minimum     

A model for creep life prediction of thin tube using strain energy density as a function of stress triaxiality under quasi-static loading employing elastic-creep & elastic-plastic-creep deformation

This paper demonstrates the application of a new multiaxial creep damage model developed by authors using stress traixiality to predict the failure time of a component made of 0.5%Cr-0.5%Mo-0.25%V low alloy steel. The model employs strain energy density and assumes that the uniaxial strain energy density of a component can be easily calculated and can be converted to multi-axial strain energy density by multiplying it to a function of stress trixiality which is a ratio of mean stress to equivalent stress. For comparison, an elastic-creep and elastic-plastic-creep finite element analysis (FEA) is performed to get multi-axial strain energy density of the component which is compared with the calculated strain energy density for both cases. The verification and application of the model are demonstrated by applying it to thin tube for which the experimental data are available. The predicted failure times by the model are compared with the experimental results. The results show that the proposed model is capable of predicting failure times of the component made of the above-mentioned material with an accuracy of 4.0%.     

Denial of service detection using dynamic time warping

With the rapid growth of security threats in computer networks, the need for developing efficient security-warning systems is substantially increasing. Distributed denial-of-service (DDoS) and DoS attacks are still among the most effective and dreadful attacks that require robust detection. In this work, we propose a new method to detect TCP DoS/DDoS attacks. Since analyzing network traffic is a promising approach, our proposed method utilizes network traffic by decomposing the TCP traffic into control and data planes and exploiting the dynamic time warping (DTW) algorithm for aligning these two planes with respect to the minimum Euclidean distance. By demonstrating that the distance between the control and data planes is considerably small for benign traffic, we exploit this characteristic for detecting attacks as outliers. An adaptive thresholding scheme is implemented by adjusting the value of the threshold in accordance with the local statistics of the median absolute deviation (MAD) of the distances between the two planes. We demonstrate the efficacy of the proposed method for detecting DoS/DDoS attacks by analyzing traffic data obtained from publicly available datasets.     

PEAβ Triggers Cognitive Decline and Amyloid Burden in a Novel Mouse Model of Alzheimer’s Disease

Understanding the physiopathology of Alzheimer’s disease (AD) has improved substantially based on studies of mouse models mimicking at least one aspect of the disease. Many transgenic lines have been established, leading to amyloidosis but lacking neurodegeneration. The aim of the current study was to generate a novel mouse model that develops neuritic plaques containing the aggressive pyroglutamate modified amyloid-β (pEAβ) species in the brain. The TAPS line was developed by intercrossing of the pEAβ-producing TBA2.1 mice with the plaque-developing line APPswe/PS1ΔE9. The phenotype of the new mouse line was characterized using immunostaining, and different cognitive and general behavioral tests. In comparison to the parental lines, TAPS animals developed an earlier onset of pathology and increased plaque load, including striatal pEAβ-positive neuritic plaques, and enhanced neuroinflammation. In addition to abnormalities in general behavior, locomotion, and exploratory behavior, TAPS mice displayed cognitive deficits in a variety of tests that were most pronounced in the fear conditioning paradigm and in spatial learning in comparison to the parental lines. In conclusion, the combination of a pEAβ- and a plaque-developing mouse model led to an accelerated amyloid pathology and cognitive decline in TAPS mice, qualifying this line as a novel amyloidosis model for future studies.     

Blind decision feedback equaliser for multichannels with commonzeros

Blind equalisation of a fractionally spaced channel (FSC) is generally difficult if all subchannels have common zeros. A new blind equalisation structure is proposed so that the uncommon part of the FSC is equalised with a fractionally spaced equaliser and the common part of the FSC is equalised with a decision feedback equaliser which operates at the baud rate