Blind Deconvolution of Ultrasonic Signals Using High-Order Spectral Analysis and Wavelets

Defect detection by ultrasonic method is limited by the pulse width. Resolution can be improved through a deconvolution process with a priori information of the pulse or by its estimation. In this paper a regularization of the Wiener filter using wavelet shrinkage is presented for the estimation of the reflectivity function. The final result shows an improved signal to noise ratio with better axial resolution.Comment: 8 pages, CIARP 2005, LNCS 377

Least-squares methods with Poissonian noise: an analysis and a comparison with the Richardson-Lucy algorithm

It is well-known that the noise associated with the collection of an astronomical image by a CCD camera is, in large part, Poissonian. One would expect, therefore, that computational approaches that incorporate this a priori information will be more effective than those that do not. The Richardson-Lucy (RL) algorithm, for example, can be viewed as a maximum-likelihood (ML) method for image deblurring when the data noise is assumed to be Poissonian. Least-squares (LS) approaches, on the other hand, arises from the assumption that the noise is Gaussian with fixed variance across pixels, which is rarely accurate. Given this, it is surprising that in many cases results obtained using LS techniques are relatively insensitive to whether the noise is Poissonian or Gaussian. Furthermore, in the presence of Poisson noise, results obtained using LS techniques are often comparable with those obtained by the RL algorithm. We seek an explanation of these phenomena via an examination of the regularization properties of particular LS algorithms. In addition, a careful analysis of the RL algorithm yields an explanation as to why it is more effective than LS approaches for star-like objects, and why it provides similar reconstructions for extended objects. We finish with a convergence analysis of the RL algorithm. Numerical results are presented throughout the paper. It is important to stress that the subject treated in this paper is not academic. In fact, in comparison with many ML algorithms, the LS algorithms are much easier to use and to implement, often provide faster convergence rates, and are much more flexible regarding the incorporation of constraints on the solution. Consequently, if little to no improvement is gained in the use of an ML approach over an LS algorithm, the latter will often be the preferred approach.Comment: High resolution images are available upon request. submitted to A&

Wave loads on open sea mooring dolphin with vertical cylinders due to regular waves

305-313Mooring dolphin is one of the components of open sea marine terminal. A thorough knowledge on wave forces on this mooring dolphin is essential for its design. Experimental investigations were carried out on wave loads on an open sea mooring dolphin with vertical slender cylinders and deck in 0.60 m water depth. The deck slab was placed at nine different elevations above and below the still water level (emerged and submerged conditions) to study the effect of deck elevation on wave loads on mooring dolphin due to regular waves. A study on single cylinder is also carried out to compare the forces on mooring dolphin with the forces on single cylinder. Wave force on single cylinder can be calculated by using Morison equation. There is no theoretical method to calculate wave forces on slender cylinders with deck, especially when the deck is in submerged condition. It is found that the in-line and transverse forces are more when the bottom of deck slab is exactly at still water level and reduce significantly when it is submerged or emerged. Mooring dolphin receives maximum slamming force when the deck is in submerged condition

How to strengthen primary health care services in Sri Lanka to meet the future challenges

Despite being a lower middle income country, Sri Lanka has achieved commendable health indicators. The main contributory factor for this achievement lies with the policy of ‘free education’ and provision of health care services free of charge to the people at the point of delivery. Despite the success, Sri Lanka is currently experiencing an epidemiological transition, where the burden of diseases has shifted from communicable diseases to the non-communicable diseases (NCDs). Strengthening primary health care (PHC) with comprehensive community-based and family-focused care is the solitary solution to address the existing health issues in Sri Lanka. Four strategic approaches have been identified. First strategy is to adopt PHC based lifecourse approach and task shifting of PHC workers to combat NCDs, while maintaining the three tier health service model. Innovative public health interventions need to be implemented through primordial, primary, secondary and tertiary prevention levels. Second strategy is to re-model and re-orient Primary Medical Care (PMC) units in the country, by establishing a ‘general practitioner (GP) system’ to link the preventive and curative PHC services at divisional level. Third strategy is to establish a referral and gatekeeping system to minimize the bypassing of PHC services. Final strategy is to introduce electronic medical record systems to minimize compartmentalization of treatment and to improve the continuum of care. Health authorities should consider these first-hand approaches in their health master plans and attempt to re-orient the health services to meet future health challenges

Gas Sensing using Terahertz Time-Domain Spectroscopy

Journal PaperA method for detection and identification of polar gases and gas mixtures based on the technique of terahertz time-domain spectroscopy is presented. This relatively new technology promises to be the first portable far-infared spectrometer, providing a means for real-time spectroscopic measurements over a broad bandwidth up to several THz. The measured time-domain waveforms can be efficiently parameterized using standard tools from signal processing, including procedures developed for speech recognition applications. These are generally more efficient than conventional methods based on Fourier analysis, and are easier to implement in a real-time sensing system. Preliminary results of real-time gas mixtures analysis using a linear predictive coding algorithm are presented. A number of possible avenues for improved signal processing schemes are discussed. In particular, the utility of a wavelet-based signal analysis for tasks such as denoising is demonstrated