Ionothermal synthesis of layered zirconium phosphates and their tribological properties in mineral oil.

In an attempt to synthesize novel zirconium phosphate materials, a series of syntheses have been performed in a deep eutectic solvent (DES), composed of tetrapropylammonium bromide (TPABr) and oxalic acid. As a result, this DES does not act as a template provider in reaction probably owing to the steric effects of the longer chains of the TPA cation, and only the α-Zr(HPO(4))(2)·H(2)O (α-ZrP) phase has been achieved. However, after organic amine was added to the initial reaction mixture in a normal way, the additives did act as a template to induce the zirconium phosphate framework. For example, with 1,4-dimethylpiperazine as an additive, a novel layered compound, [C(6)H(16)N(2)](0.5)Zr(H(0.5)PO(4))(2)·H(2)O (denoted as ZrPO(4)-DES8) was obtained. Its structure was determined from single-crystal X-ray diffraction (XRD) data and consists of zirconium phosphate layers with the protonated 1,4-dimethylpiperazine and water molecules in between. Interestingly, the two layered materials as additives in a liquid lubricant exhibit excellent friction behavior with higher load-carrying and antiwear capacities in comparison to typical lubricant additives such as MoS(2) and graphite, increase the P(B) value of the base oil by 27.2% and 8.5%, and decrease the wear scar diameter of the base oil by 43% and 36%, respectively. Scanning electron microscopy, XRD, and energy-dispersive X-ray spectrometry are used to investigate the lubricant behavior of those materials.

Influence of anisotropy on peri-implant stress and strain in complete mandible model from CT.

This paper reveals the influence of elastic anisotropy for the peri-implant stress and strain in personalized mandible. First, from CT data, the individual geometry of the complete range of mandible was well reproduced, also the separation between cortical and cancellous bone. Then, by an ad hoc automatic mesh generator integrated with anisotropic material assignment function, high quality anisotropic finite element model of the complete mandible was created, with two standard threaded implants embedded in posterior zone. The values of principal stress and strain in surrounding bone were evaluated under buccolingual oblique loading, and compared to that of the same FE model with equivalent isotropic material. Results of the analyses demonstrated that the percentage increase of stress and strain in anisotropic case reached up to 70%. It is concluded that anisotropy has significant effects on peri-implant stress and strain and careful consideration should be given to its use in biomechanical FE studies.

Anisotropic finite element modeling for patient-specific mandible.

This paper presents an ad hoc modular software tool to quasi-automatically generate patient-specific three-dimensional (3D) finite element (FE) model of the human mandible. The main task is taking into account the complex geometry of the individual mandible, as well as the inherent highly anisotropic material law. At first, by computed tomography data (CT), the individual geometry of the complete range of mandible was well reproduced, also the separation between cortical and cancellous bone. Then, taking advantage of the inherent shape nature as 'curve' long bone, the algorithm employed a pair of B-spline curves running along the entire upper and lower mandible borders as auxiliary baselines, whose directions are also compatible with that of the trajectory of maximum material stiffness throughout the cortical bone of the mandible. And under the guidance of this pair of auxiliary baselines, a sequence of B-spline surfaces were interpolated adaptively as curve cross-sections to cut the original geometry. Following, based on the produced curve contours and the corresponding curve cross-section surfaces, quite well structured FE volume meshes were constructed, as well as the inherent trajectory vector fields of the anisotropic material (orthotropic for cortical bone and transversely isotropic for cancellous bone). Finally, a sensitivity analysis comprising various 3D FE simulations was carried out to reveal the relevance of elastic anisotropy for the load carrying behavior of the mandible.

Distributed collaborative CAD system based on Web Service.

This paper presents a novel Web Service based distributed collaborative CAD system employing feature as its collaborative design element and uses XML to define feature operations and communication protocol between the server and the client. To reduce network load and increase response ability of the system, the feature information is updated incrementally on the client. The system supports collaborative designing on heterogeneous platforms. Its framework and communication protocols are analyzed in detail. The experimental results from the developed prototype system showed that it can effectively support collaborative design under the distributed environment.

Intersections of two offset parametric surfaces based on topology analysis.

Conventional methods for solving intersections between two offset parametric surfaces often include iteratively using computationally expensive SSI (surface/surface intersections) algorithm. In addition, these methods ignore the relations between the intersection curves of parametric surfaces with different offset distances. The algorithm presented in this paper, makes full use of the topological relations between different intersection loops and calculates intersection loops with the help of previously calculated intersection loops. It first pre-processes two parametric surfaces to obtain the characteristic points, called topology transition points (TTPs), which can help in the subsequent finding of the topologies of the intersection curves. Then these points are categorized into several distinct groups, and we can determine the calculation strategy for searching initial points by analyzing the properties of these TTPs on the surfaces. Hence, all intersection curves can be marched from initial points by the tracing algorithm. The proposed algorithm could calculate intersection curves robustly and effectively, and has been tested to be capable of overcoming the degenerate conditions such as loop and singularities leaking that occur frequently in conventional algorithms.

Efficient volume preserving approach for skeleton-based implicit surfaces.

This paper presents an efficient way to preserve the volume of implicit surfaces generated by skeletons. Recursive subdivision is used to efficiently calculate the volume. The criterion for subdivision is obtained by using the property of density functions and treating different types of skeletons respectively to get accurate minimum and maximum distances from a cube to a skeleton. Compared with the criterion generated by other ways such as using traditional Interval Analysis, Affine Arithmetic, or Lipschitz condition, our approach is much better both in speed and accuracy.

Solving geometric constraints with genetic simulated annealing algorithm.

This paper applies genetic simulated annealing algorithm (SAGA) to solving geometric constraint problems. This method makes full use of the advantages of SAGA and can handle under-/over- constraint problems naturally. It has advantages (due to its not being sensitive to the initial values) over the Newton-Raphson method, and its yielding of multiple solutions, is an advantage over other optimal methods for multi-solution constraint system. Our experiments have proved the robustness and efficiency of this method.

Building a highly available and intrusion tolerant Database Security and Protection System (DSPS).

Database Security and Protection System (DSPS) is a security platform for fighting malicious DBMS. The security and performance are critical to DSPS. The authors suggested a key management scheme by combining the server group structure to improve availability and the key distribution structure needed by proactive security. This paper detailed the implementation of proactive security in DSPS. After thorough performance analysis, the authors concluded that the performance difference between the replicated mechanism and proactive mechanism becomes smaller and smaller with increasing number of concurrent connections; and that proactive security is very useful and practical for large, critical applications.