On the low frequency acoustic properties of novel multifunctional honeycomb sandwich panels with micro-perforated faceplates

This paper explores further possibilities of structurally-efficient honeycomb sandwich panels by replacing one of the faceplates with the perforated faceplate from the viewpoint of sound absorption coefficient (SAC) as well as sound transmission loss (STL). An analytical model is presented to calculate both the STL and SAC, with the displacements of the two faceplates assumed identical at frequencies below the faceplate resonance frequency. Influences of core configuration are investigated by comparing different honeycomb core designs. Finite element (FE) models are subsequently developed to validate the proposed analytical model, with agreement achieved. Subsequently, parametric surveys, including the influences of perforation ratio, pore size and core configuration on STL and SAC, are conducted based on the analytical model. Unlike classical honeycomb sandwich panels which are poor sound absorbers, honeycomb sandwiches with perforated faceplates lead to high SAC at low frequencies, which in turn brings about increment in the low frequency STL. Moreover, sandwich panels with triangular cores are found to have the lowest peak frequency in the STL and SAC curves compared with the other kinds of sandwich panels having the same effective mass and perforations

Anisotropic acoustical properties of sintered fibrous metals

A combined theoretical and experimental study is carried out to investigate the anisotropic acoustic properties of sintered fibrous metals. In the theoretical model, based on the transversal and longitudinal dynamic mass densities and effective bulk modulus of randomly placed parallel fibers, the dynamic mass densities and effective dynamic bulk modulus of a sintered fibrous metal in the direction normal and parallel to its surface are obtained. Sound absorption coefficient, sound speed and attenuation coefficient in each of the two directions are calculated once the dynamic mass densities and effective dynamic bulk modulus are determined. For validation, experimental measurements are performed, with good agreement between theoretical prediction and measurement data achieved. Subsequent numerical investigations focus on the influence of fiber diameter and porosity on the anisotropic acoustical properties of the sintered fibrous metal. The sintered fibrous metal exhibits better sound absorption/attenuation performance in the parallel direction than in the normal direction. The anisotropy in acoustical properties increases with decreasing fiber diameter and porosity due mainly to increasing interactions between adjacent fibers

Small perforations in corrugated sandwich panel significantly enhance low frequency sound absorption and transmission loss

Numerical and experimental investigations are performed to evaluate the low frequency sound absorption coefficient (SAC) and sound transmission loss (STL) of corrugated sandwich panels with different perforation configurations, including perforations in one of the face plates, in the corrugated core, and in both the face plate and the corrugated core. Finite element (FE) models are constructed with considerations of acoustic-structure interactions and viscous and thermal energy dissipations inside the perforations. The validity of FE calculations is checked against experimental measurements with the tested samples provided by additive manufacturing. Compared with the classical corrugated sandwich without perforation, the corrugated sandwich with perforated pores in one of its face plate not only exhibits a higher SAC at low frequencies but also a better STL as a consequence of the enlarged SAC. The influences of perforation diameter and perforation ratio on the vibroacoustic performance of the sandwich are also explored. For a corrugated sandwich with uniform perforations, the acoustical resonance frequencies and bandwidth in its SAC and STL curves decrease with increasing pore diameter and decreasing perforation ratio. Non-uniform perforation diameters and perforation ratios result in larger bandwidth and lower acoustical resonance frequencies relative to the case of uniform perforations. The proposed perforated sandwich panels with corrugated cores are attractive ultralightweight structures for multifunctional applications such as simultaneous load-bearing, energy absorption, sound proofing and sound absorption

Effects of free surface and heterogeneous residual internal stress on stress-driven grain growth in nanocrystalline metals

By reevaluating the experimental study of Zhang et al. (2005), here we demonstrate that the extent of grain growth, previously proposed to be solely driven by external stress, may have been significantly overestimated. A new physical mechanism, termed as free surface assisted stress-driven grain growth (or self-mechanical annealing), is proposed and discussed in detail. Representing the cooperative effect of free surface and heterogeneous residual internal stress, the proposed mechanism is considered more favorable than the traditional pure stress-driven mechanism for interpreting the abnormal grain growth widely observed in deforming nanocrystalline metals at room temperature

Fast simultaneous detection of K-RAS mutations in colorectal cancer

<p>Abstract</p> <p>Background</p> <p><it>RAS </it>genes acquire the most common somatic gain-of-function mutations in human cancer, and almost all of these mutations are located at codons 12, 13, 61, and 146.</p> <p>Methods</p> <p>We present a method for detecting these <it>K-RAS </it>hotspot mutations in 228 cases of colorectal cancer. The protocol is based on the multiplex amplification of exons 2, 3 and 4 in a single tube, followed by primer extension of the PCR products using various sizes of primers to detect base changes at codons 12, 13, 61 and 146. We compared the clinicopathological data of colorectal cancer patients with the <it>K-RAS </it>mutation status.</p> <p>Results</p> <p><it>K-RAS </it>mutation occurred in 36% (83/228) of our colorectal cancer cases. Univariate analysis revealed a significant association between <it>K-RAS </it>mutation at codon 12 of exon 2 and poor 5-year survival (p = 0.023) and lymph node involvement (p = 0.048). Also, <it>K-RAS </it>mutation at codon 13 of exon 2 correlates with the size of the tumor (p = 0.03). Multivariate analysis adjusted for tumor size, histologic grade, and lymph node metastasis also indicated <it>K-RAS </it>mutations at codon 12 and 13 of exon 2 correlate significantly with overall survival (p = 0.002 and 0.025). No association was observed between codon 61 and 146 and clinicopathological features.</p> <p>Conclusion</p> <p>We demonstrated a simple and fast way to identify <it>K-RAS </it>mutation.</p

Group testing with Random Pools: Phase Transitions and Optimal Strategy

The problem of Group Testing is to identify defective items out of a set of objects by means of pool queries of the form "Does the pool contain at least a defective?". The aim is of course to perform detection with the fewest possible queries, a problem which has relevant practical applications in different fields including molecular biology and computer science. Here we study GT in the probabilistic setting focusing on the regime of small defective probability and large number of objects, $p \to 0$ and $N \to \infty$. We construct and analyze one-stage algorithms for which we establish the occurrence of a non-detection/detection phase transition resulting in a sharp threshold, $\bar M$, for the number of tests. By optimizing the pool design we construct algorithms whose detection threshold follows the optimal scaling $\bar M\propto Np|\log p|$. Then we consider two-stages algorithms and analyze their performance for different choices of the first stage pools. In particular, via a proper random choice of the pools, we construct algorithms which attain the optimal value (previously determined in Ref. [16]) for the mean number of tests required for complete detection. We finally discuss the optimal pool design in the case of finite $p$

Rotational degree-of-freedom synthesis: An optimised finite difference method for non-exact data

Measuring the rotational dynamic behaviour of a structure is important for many areas of dynamics such as passive vibration control, acoustics, and model updating. Specialist and dedicated equipment is often needed, unless the rotational degree-of-freedom is synthesised based upon translational data. However, this involves numerically differentiating the translational mode shapes to approximate the rotational modes, for example using a finite difference algorithm. A key challenge with this approach is choosing the measurement spacing between the data points, an issue which has often been overlooked in the published literature. The present contribution will for the first time prove that the use of a finite difference approach can be unstable when using non-exact measured data and a small measurement spacing, for beam-like structures. Then, a generalised analytical error analysis is used to propose an optimised measurement spacing, which balances the numerical error of the finite difference equation with the propagation error from the perturbed data. The approach is demonstrated using both numerical and experimental investigations. It is shown that by obtaining a small number of test measurements it is possible to optimise the measurement accuracy, without any further assumptions on the boundary conditions of the structure

Surgical Treatment of Kawasaki Disease with Intestinal Pseudo-obstruction

A 5-year-old boy suffering from abdominal pain accompanied by a fever of up to 39.5 degrees C for 2 days was admitted to the hospital. Although Flomoxef was administered following admission, the boy's fever persisted and abdominal distension gradually worsened. On the 4th day, dry lips, red eyes and a strawberry tongue were noted. An echocardiogram revealed pericoronary enhancement with mild mitral valve regurgitation and a small degree of pericardial effusion, characteristics compatible with Kawasaki disease. Although intravenous immunoglobulin was administered, the fever and abdominal distension persisted. On the 8th day, a pediatric surgeon was consulted and an exploratory laparotomy was arranged. During the operation, intestinal pseudo-obstruction and fibrin coatings around the intestine near the splenic flexure were found. A colostomy was performed for decompression of the dilated bowel and a biopsy of the lymph node surrounding the splenic flexure was taken. The fever subsided dramatically after decompression of the bowel and the recovery course was uneventful. The pathologic report revealed necrotic lymphadenitis. We report this rare case and review the literature

Feature recognition applications in mesh generation

The use of feature recognition as part of an overall decomposition-based hexahedral meshing approach is described in this paper. The meshing approach consists of feature recognition, using a c-loop or hybrid c-loop method, and the use of cutting surfaces to decompose the solid model. These steps are part of an iterative process, which proceeds either until no more features can be recognized or until the model has been completely decomposed into meshable sub-volumes. This method can greatly reduce the time required to generate an all-hexahedral mesh, either through the use of more efficient meshing algorithms on more of the geometry or by reducing the amount of manual decomposition required to mesh a volume