Monte Carlo simulation of B2-L2<Subscript>1</Subscript> ordering transitions in Au-Cu-Al alloy systems

The B2-L2₁ ordering transitions in Au-Cu-Al shape-memory alloys are studied by the Monte Carlo exchange simulations, where a set of the first, the second and the third nearest-neighbor mixing potentials for Cu-Al in the Au-Cu-Al alloys are calculated from first principals using the Connolly-Williams methods. To ensure the phase stability of the β-Au-Cu-Al, the investigation includes the range of compositions Au₂Cu_1−x Al_1+x (−0.15 ⩽ x ⩽ 0.15). The B2-L2₁ transition temperatures are predicted, and are in agreement with the experimental results. The atomic ordering around vacancy of the L2₁ structure is further discussed.     

Multi-element ultrasound phased array applicator for the ablation of deep-seated tissue

High-intensity focused ultrasound (HIFU) has attracted increasing interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity. A 90-element HIFU spherical phased array applicator operated at 1MHz has been developed for deep tissue ablation. The spherical array with a 5 cm wide central hole has a 21 cm diameter and an 18 cm radius of curvature. Annular element distribution with unequal element spacing is used to reduce the number of elements. The array is constructed with piezoelectric lead zirconate titanate (PZT-8) circular elements that are 1.4 cm in diameter and have a wall with thickness of 0.2 cm. The array offers an effective ablating depth of at least 8 cm in the tissue for both simulations and ex vivo experiments. The simulations demonstrate that the developed array can steer the focus with good quality of intensity distributions up to 6mm off center over ranges from 17 to 21 cm when the water depth is set at 11 cm. We also present the beam focusing capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications. These results indicate that the developed array is ideal for the ablation of deep-seated tissue.     

Optimization of pellet production process parameters in grate using simulation results

The objective of this paper is to optimize the parameters of pellet drying and preheating process in grate. A mathematical model of drying and preheating is developed, and is verified by the experiments. Further, the operating parameters of wind temperature, wind speed, grate speed and bed depth etc. are investigated through the orthogonal method using the simulation results. And a relationship of drying, preheating effects and operating parameters is achieved. The results show that the optimization effect can be achieved in the given range when air velocity is about 3.0 m/s and temperature is about 300, 500, 800, and 1 100 °C in the updraft drying zone, downdraft drying zone, preheating I zone, and preheating II zone respectively. The work is help for saving energy and reducing emissions in pellet induration.     

An information-based color feature representation and its application in detecting adult images

For many image classification tasks, color histogram is usually employed as an important “signature” to describe the color distribution of the image and infer the image content. However, most traditional color histograms cannot achieve satisfactory results in many image classification systems. In order to improve the accuracy and reduce the computational complexity of the classification task, an information-based color feature representation is proposed in this paper. The mutual information between the feature and the class label is adopted to evaluate the discriminative power of the feature. A novel quantization scheme is presented, which removes the redundant color components and combines the adjacent components together to generate a new feature to maximize the discriminative ability. An iterative algorithm is performed to derive the color space quantization and color feature generation. In order to illustrate the effectiveness of the proposed color representation, a specific image classification task, i.e., differentiating the adult images from benign ones, is employed. Experimental results show that our color feature achieves better classification performance and better efficiency compared with the traditional color histogram.     

Structure-borne sound attenuation at corner interface with dynamic vibration absorber attached

Structure-borne sound attenuation at corner interface of two plates with dynamic vibration absorber attached is investigated by wave approach. Equations governing transmission and reflection coefficients are deduced by introducing some non-dimensional coefficients, which help to reveal the physical sense inside and to simplify the analysis. Numerical investigation on vibration energy transmission of bending wave is carried out as well. The results from measurement and prediction show almost the same trends in the simplified experiment. It is found that energy transmission at corner interface depends greatly on whether the dynamic vibration absorber attached acts at resonance and is relatively lower right after the nature frequency of dynamic vibration absorber. Furthermore, the dynamic vibration absorber attached provides less energy transmission of bending wave than blocking mass at the end of “passing band”.     

Accurate 3D reconstruction of subject-specific knee finite element model to simulate the articular cartilage defects

The biomechanical relationship between the articular cartilage defect and knee osteoarthritis (OA) has not been clearly defined. This study presents a 3D knee finite element model (FEM) to determine the effect of cartilage defects on the stress distribution around the defect rim. The complete knee FEM, which includes bones, articular cartilages, menisci and ligaments, is developed from computed tomography and magnetic resonance images. This FEM then is validated and used to simulate femoral cartilage defects. Based on the obtained results, it is confirmed that the 3D knee FEM is reconstructed with high-fidelity level and can faithfully predict the knee contact behavior. Cartilage defects drastically affect the stress distribution on articular cartilages. When the defect size was smaller than 1.00 cm², the stress elevation and redistribution were found undistinguishable. However, significant stress elevation and redistribution were detected due to the large defect sizes (⩾1.00 cm²). This alteration of stress distribution has important implications relating to the progression of cartilage defect to OA in the human knee joint.     

A new algorithm for non-newtonian flow and its application in mould filling process

The simulation of injection molding process requires a stable algorithm to model the molten polymer with non-isothermal non-Newtonian property. In this paper, a staggered and iterative scheme is particularly designed to solve the velocity-pressure-temperature variables. In consideration of the polymer characteristic of high viscosity and low thermal conductivity, the non-Newtonian momentum-mass conservation equations are solved by the Crank-Nicolson method based split (CNBS) scheme, and the energy conservation equation with convective character is discretized by the characteristic Galerkin (CG) method. In addition, an arbitrary Lagrangian Eulerian (ALE) free surface tracking and mesh generation method is introduced to catch the front of the fluid flow. The efficiency of the proposed scheme is demonstrated by numerical experiments including a lid-driven cavity flow problem and an injection molding problem.     

Numerical simulation of multi-pass rolling force and temperature field of plate steel during hot rolling

Rolling force and temperature field are important parameters in the hot rolling process of plate steel. Most researchers use ANSYS/LS-DYNA and MSC.Marc to simulate the hot rolling process, however, software DEFORM-3D is not used widely in this field. Therefore, in this study, the commercially available finite element analysis software DEFORM-3D is used to simulate the distribution of rolling force, stress-effective, strain-effective and temperature field during the hot rolling process of plate steel with the size of 0.220m×2.070m×1.904m. Both the simulated rolling force and temperature of the multi-pass are compared with the measured results. It is shown that the simulated values by the finite element method are approximate to the measured values in the hot rolling of plate steel. So the simulation can provide an important reference and optimization to make rolling process and parameters in steel factory.     

Numerical simulation of fluid flow caused by buoyancy forces during vacuum arc remelting process

The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0 software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.     

Improved preimage attack on 3-pass HAVAL

HAVAL is a hash function proposed by Zheng et al. in 1992, including 3-, 4- and 5-pass versions. We improve pseudo-preimage and preimage attacks on 3-pass HAVAL at the complexity of 2¹⁷² and 2^209.6, respectively, as compared to the previous best known results: 2¹⁹² and 2²²⁵ by Sasaki et al. in 2008. We extend the skip interval for partial-patching and apply the initial structure technique to find the better message chunks, and combine the indirect-partial-matching, partial-fixing and multi-neutral-word partial-fixing techniques to improve the attacks based on the meet-in-the-middle method. These are the best pseudo-preimage and preimage attacks on 3-pass HAVAL.