A versatile wavelet domain noise filtration technique for medical imaging

In this paper, we propose a robust wavelet domain method for noise filtering in medical images. The proposed method adapts itself to various types of image noise as well as to the preference of the medical expert; a single parameter can be used to balance the preservation of (expert-dependent) relevant details against the degree of noise reduction. The algorithm exploits generally valid knowledge about the correlation of significant image features across the resolution scales to perform a preliminary coefficient classification. This preliminary coefficient classification is used to empirically estimate the statistical distributions of the coefficients that represent useful image features on the one hand and mainly noise on the other. The adaptation to the spatial context in the image is achieved by using a wavelet domain indicator of the local spatial activity. The proposed method is of low complexity, both in its implementation and execution time. The results demonstrate its usefulness for noise suppression in medical ultrasound and magnetic resonance imaging. In these applications, the proposed method clearly outperforms single-resolution spatially adaptive algorithms, in terms of quantitative performance measures as well as in terms of visual quality of the images.     

Practical Assessment of Electronic Water Treatment for the Prevention of Fouling

Fouling or scaling, i.e., the occurrence of deposits on tubes, heat exchangers, and other devices, is a common problem in industrial and domestic processes. Many anti‐fouling techniques exist, both chemically and non‐chemically. The efficiency of non‐chemical methods is still controversial, although the use of these devices is already widespread in industry. In this contribution, a case study is presented in which the operation of such a device is demonstrated. The electronic water treatment device under study was connected to a 2 m‐long copper tube immersed in a water bath with a temperature of 65 °C. A short‐term experiment revealed that the device did not alter the water chemistry and that locally, fouling was prevented by the device. However, the potential for fouling further downstream was not reduced. A long‐term experiment further confirmed the findings of the short‐term experiment showing that locally, the device has an anti‐fouling action as a significant increase in weight was observed when the device was switched off and a significant decrease in weight was observed when the device was switched on.     

On Stress Intensity Factors of Multiple Cracks at Small Distances in 2-D Problems

In the present work a method is proposed to predict stress intensity factors (SIFs) of strongly interacting cracks at spacings that are substantially smaller than crack lengths. The method is intended for applications where cracks are observed in stack-like/staggered arrangements as in damage patterns of some natural materials with dense lamellar microstructures. The new calculation procedure is inspired by the analytical method of Kachanov (1987) that due to its simplicity has shown to be a powerful tool for analysis of crack interactions. Although in 3-D the accuracy of Kachanov’s method remains good at quite close spacings, in 2-D problems it, however, quickly drops as the distance between cracks decreases, underestimating the effect of crack interactions, especially in ordered staggered arrangements. In this work we introduce new modeling assumptions that are suited for problems where stress fields have high gradients – a typical situation in the case of closely spaced parallel cracks. The accuracy of the method is examined on the example of two stacked cracks. The use of SIFs for estimation of material elastic compliance is also discussed.     

Homogenization of metamaterials using full-wave simulations

We present a full-wave homogenization method to determine the effective material parameters of metamaterials by considering a spherical piece of metamaterial. We use a T-matrix approach that is accelerated by a multilevel fast multipole method that is stable at low frequencies. To determine the T-matrix of one inclusion in the metamaterial a Method of Moments surface integral equation is used that is also accelerated using another multilevel fast multipole method that is stable at low frequencies. We also derive a new closed-form expression to extract the effective material parameters from the T-matrix of the spherical piece of material. Examples verify the accuracy and limitations of the method. We show results for metamaterials comprising more than 40,000 particles.     

Stability effects associated with the introduction of a partial and a complete Ca2+-binding site into human lysozyme

Two mutants of human lysozyme were synthesized. Mutant A92D,in which Ala92 was substituted by Asp, contains a partial Ca²⁺-bindingsite and mutant M4, in which Ala83, Gm86, Asn88 and Ala92 werereplaced by Lys, Asp, Asp and Asp respectively, contains thecomplete Ca -binding site of bovine a-lactalbumin. The Ca²⁺-bindingconstants of wild type human lysozyme and of mutants A92D andM4, measured at 25C and pH 7.5, were 2(1) x 102 M"1, 8(2)x l^M"1 and 9(0.5) x 10* M"1 respectively. Information gatheredfrom mkrocalorimetrk and CD spectro-scopic measurements indicatesthat the conformational changes of the M4 mutant lysozyme, inducedby Ca²⁺ binding, are smaller than those observed for bovinea-lactalbumin and for the Ca²⁺-binding equine lysozyme. At pH4.5, the thermostability of both the apo and Ca²⁺ forms of theA92D human was decreased in comparison with that of native humanlysozyme. In particular, within the apo form of this mutantan a-helix-containing sequence was destabilized. In contrast,at the same pH the thermostability of the apo and Ca²⁺ formsof the M4 mutant lysozyme was increased. The e-ammonium groupof the Lys83 side chain is assumed to be responsible for thestabilization of the apo form of this mutant.     

Modelling the polypeptide backbone with 'spare parts' from known protein structures

An automatic procedure for building a protein polyalanine backbonefrom C positions and ‘spare parts’ retrieved froma data base of 66 high-resolution protein structures is described.Protein backbones are constructed from over-lapping fragmentsof variable length, which allows the backbone of regular secondarystructure elements to be built in one block. The procedure isshown to yield backbones which compare very favourably withthose from highly refined X-ray structures (r.m.s. deviationbetween generated and crystal structures <lÅ). Themethod is furthermore quite insensitive to experimental errorsin C positions as well as to the size of the data base, andis seen to yield valuable insight into the relationships betweensequence and 3-D structure: one example on triose phosphateisomerase, a ß-barrel protein, shows that ßloops can be considered as structurally more uncommon than ßloops. The ‘spare parts’ approach is also foundto be useful for general-purpose modelling of local structuralchanges produced by insertion or deletion of residues. It should,however, be used with caution. Crude selection criteria basedsolely on fragment length and geometric fit to the loop baseregions yield realistic backbones in about two-thirds of thetest cases (r.m.s. deviations from refined crystal structure{small tilde}lÅ). In the remaining cases, sequence information,in particular the presence of glycine residues which tend toadopt more unusual backbone conformations, must be consideredto obtain comparable results.     

On modelling of damage evolution in textile composites on meso-level via property degradation approach

The continuous damage mechanics (CDM) approach is a popular tool for modelling of damage evolution in textile composites on the meso-level. It is based on the assumption that a material with defects can be replaced by a fictitious material with no defects but with degraded elastic constants. In such way the presence of defects is only reflected in the material elastic properties and damage evolution is recorded through the loss of these properties. The CDM approach incorporated into finite element analysis often predicts unphysically wide damage zones and in some cases failure across yarns – findings that are not supported by experimental data. The current work is geared toward identifying the source of inconsistencies between experiment and modelling by revisiting basic assumptions of CDM. A test problem is proposed to illustrate a break down of the CDM approach where a single crack-like defect in a yarn is modelled as an inhomogeneity with elastic constants reduced according to Murakami–Ohno model. It is shown that CDM in combination with local stress analysis of failure may predict a different direction of damage evolution as well as an incorrect failure mode in comparison with the crack problem. We also investigate whether the Murakami–Ohno model adopted for calculation of properties of a fictitious inhomogeneity contributes to the unphysical results. For this we compare contributions of a crack and an inhomogeneity into material elastic response. A new property degradation procedure is suggested (referred here as an effective elastic response model) where the size of an inhomogeneity and properties of the surrounding material are taken into account.     

Using Bayesian neural networks with ARD input selection to detect malignant ovarian masses prior to surgery

In this paper, we applied Bayesian multi-layer perceptrons (MLP) using the evidence procedure to predict malignancy of ovarian masses in a large (n = 1,066) multi-centre data set. Automatic relevance determination (ARD) was used to select the most relevant inputs. Fivefold cross-validation (5CV) and repeated 5CV was used to select the optimal combination of input set and number of hidden neurons. Results indicate good performance of the models with area under the receiver operating characteristic curve values of 0.93–0.94 on independent data. Comparison with a linear benchmark model and a previously developed logistic regression model shows that the present problem is very well linearly separable. A resampling analysis further shows that the number of hidden neurons specified in the ARD analyses for input selection may influence model performance. This paper shows that Bayesian MLPs, although not frequently used, are a useful tool for detecting malignant ovarian tumours.     

Efficient Semitransparent Solar Cells with High NIR Responsiveness Enabled by a Small‐Bandgap Electron Acceptor

Inspired by the remarkable promotion of power conversion efficiency (PCE), commercial applications of organic photovoltaics (OPVs) can be foreseen in near future. One of the most promising applications is semitransparent (ST) solar cells that can be utilized in value‐added applications such as energy‐harvesting windows. However, the single‐junction STOPVs utilizing fullerene acceptors show relatively low PCEs of 4%–6% due to the limited sunlight absorption because it is a dilemma that more photons need to be harvested in UV–vis–near‐infrared (NIR) region to generate high photocurrent, which leads to the significant reduction of device transparency. This study describes the development of a new small‐bandgap electron‐acceptor material ATT‐2, which shows a strong NIR absorption between 600 and 940 nm with an E _g^opt of 1.32 eV. By combining with PTB7‐Th, the as‐cast OPVs yield PCEs of up to 9.58% with a fill factor of 0.63, an open‐circuit voltage of 0.73 V, and a very high short‐circuit current of 20.75 mA cm^?2. Owing to the favorable complementary absorption of low‐bangap PTB7‐Th and small‐bandgap ATT‐2 in NIR region, the proof‐of‐concept STOPVs show the highest PCE of 7.7% so far reported for single‐junction STOPVs with a high transparency of 37%.     

Delayed Attentional Engagement in the Attentional Blink.

Observers often miss the 2nd of 2 visual targets (first target [T1] and second target [T2]) when these targets are presented closely in time; the attentional blink (AB). The authors hypothesized that the AB occurs because the attentional response to T2 is delayed by T1 processing, causing T2 to lose a competition for attention to the item that follows it. The authors investigated this hypothesis by determining whether the AB is attenuated when T2 is precued. The results from 4 experiments showed that the duration and magnitude of the AB were substantially reduced when T2 was precued. The observed improvement in T2 report did not occur at the expense of T1 report, suggesting that processing of T1 was already completed or was at least protected when the cue was presented. The authors conclude that, during the AB, there is a delay between detection and the selection of target candidates for consolidation in short-term memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)