Microstructure and chemistry affects apatite nucleation on calcium phosphate bone graft substitutes

The bioactivity of calcium phosphate bone grafts of varying chemistry and strut-porosity was compared by determining the rate of formation of hydroxycarbonate apatite crystals on the material surface after being soaked in simulated body fluid for up to 30 days. Three groups of silicate-substituted hydroxyapatite material were tested, with each group comprising a different quantity of strut-porosity (23, 32, and 46 % volume). A commercially available porous β-tricalcium phosphate bone graft substitute was tested for comparison. Results indicate that strut-porosity of a material affects the potential for formation of a precursor to bone-like apatite and further confirms previous findings that β-tricalcium phosphate is less bioactive than hydroxyapatite.     

High-speed cornering by CNC machines under prescribed bounds on axis accelerations and toolpath contour error

To exactly execute a sharp corner in the toolpath, the feedrate of a CNC machine must instantaneously drop to zero at that point. This constraint is problematic in the context of high-speed machining, since it incurs very high deceleration/acceleration rates near sharp corners, which increase the total machining time, and may incur significant path deviations (contour errors) at these points. A strategy for negotiating sharp corners in high-speed machining is proposed herein, based upon a priori toolpath/feedrate modifications in their vicinity. Each corner is smoothed by replacing a subset of the path that contains it with a conic “splice” segment, deviating from the exact corner by no more than a prescribed tolerance ?, along which the square of the feedrate is specified as a Bernstein-form polynomial. The problem of determining the fastest traversal of the conic segments under known axis acceleration bounds can then be formulated as a constrained optimization problem, and by exploiting some well-known properties of Bernstein-form polynomials this can be approximated by a simple linear programming task. Some computed examples are presented to illustrate the implementation and performance of the high-speed cornering strategy.     

Solution of inverse dynamics problems for contour error minimization in CNC machines

For CNC machines governed by typical feedback controllers, the problem of compensating for inertia and damping of the machine axes is solved by a priori modifications to the commanded path geometry. Standard second-order models of axis dynamics are expressed in terms of the path parameter ξ rather than the time t as independent variable, incurring ordinary differential equations with polynomial coefficients. For a commanded path specified as a Pythagorean-hodograph curve R(ξ) and a P controller, a modified path $\hat{\bf R}(\xi)$ can be determined as a rational Bézier curve, that precisely compensates for the axis inertia and damping, and thus (theoretically) achieves zero contour error. For PI, PID, or P–PI controllers, exact closed-form solutions for $\hat{\bf R}(\xi)$ are no longer possible, but polynomial approximations may be computed in the numerically stable Bernstein basis on ξ?∈?[ 0,1 ]. The inverse-dynamics path modification procedure is applicable to both constant feedrates and variable feedrates defined by polynomial functions V(ξ) of the curve parameter. The method is described in the general context of PID controllers, and its implementation is then demonstrated for both P and PI controllers, governing motion along paths with extreme variations of curvature and/or parametric speed.     

黑川纪章在中国

黑川纪章是日本著名建筑师,其设计作品遍布日本和世界其他城市,他提出的"共生"理论更是影响了几代学人。在其事业处于巅峰的1980年代,黑川纪章来到中国,开启了他在中国20年的设计历程。通过回顾黑川纪章在中国的3个代表性作品,试图为中国和日本当代建筑研究提供新的材料和佐证。     

Learning to live in a smart home

ABSTRACT

Smart homes promise to significantly enhance domestic comfort, convenience, security and leisure whilst simultaneously reducing energy use through optimized home energy management. Their ability to achieve these multiple aims rests fundamentally on how they are used by householders, yet very little is currently known about this topic. The few studies that have explored the use of smart homes have tended to focus on special-interest groups and be quite short-term. This paper reports on new in-depth qualitative data that explore the domestication of a range of smart home technologies in 10 households participating in a nine-month field trial. Four core themes emerge: (1) smart home technologies are both technically and socially disruptive; (2) smart homes require forms of adaptation and familiarization from householders that can limit their use; (3) learning to use smart home technologies is a demanding and time-consuming task for which there is currently very little support available; and (4) there is little evidence that smart home technologies will generate substantial energy savings and, indeed, there is a risk that they may generate forms of energy intensification. The paper concludes by discussing the implications of these findings for policy, design and further research.     

在水一方——2012年台湾建筑奖侧记

台湾建筑奖创立于1979年,是台湾岛内最具信誉的建筑奖.34年来共评选出百余奖项,成为见证台湾建筑发展的重要里程碑台湾建筑不懈的追求,使其在亚洲和大中华地区独树帜.笔者参与了2012年台湾建筑奖的评选活动,在此分享所见所感,希望加强两岸三地的交流和整合.     

地铁站上的漂浮城岛——香港九龙站发展案例研究

通过聚焦九龙机铁站并观察其巨构建筑的特征来考察香港九龙站地区的发展计划案,分析巨构建筑的原型并将其与九龙机铁站项目进行对比.总结巨构建筑和香港地铁网络站点结合的实践,并指出巨构建筑在亚洲城市中的空间分布特征,试图在建筑语境下建立起评判的标准.