Comparison of coordinate measurement precision of different landmark types on human crania using a 3D laser scanner and a 3D digitiser: Implications for applications of digital morphometrics

A total of 11 340 Cartesian coordinates of 42 homologous landmarks on five excavated human crania were recorded by three observers using a three‐dimensional (3D) digitiser and computer models created with a 3D laser scanner. The aim was to compare the errors of the coordinate data of landmarks of different types recorded with these two techniques. The results showed that digitiser‐based and 3D model‐based coordinate measurements had overall standard deviations of, respectively, ±0.79 and ±1.05 mm. However, the 3D digitiser yielded the most precise coordinate data for landmarks defined primarily by biological criteria (Type I landmarks), while the 3D laser scanner models yielded the most precise coordinate data for landmarks defined primarily by geometric criteria (Type III landmarks). These findings are likely to influence the research design of future craniometric studies, as they indicate that the suitability of certain landmark types as reference points for geometric operations, such as partial Procrustes analysis, depends on the method by which they are measured. This information is particularly important for retrospective research or for combined databases such as FORDISC or CRANID, which may integrate different types of landmarks recorded by different researchers and/or instruments. Crania displaying poor preservation and surface discoloration yielded larger measurement errors, especially for the 3D model measurements. This is not surprising given that landmarks on 3D models cannot be located using tactile means, but have to be located solely on a visual basis. Nonetheless, even though the digitiser measurements exhibit an overall precision slightly greater than the 3D model measurements, both techniques yield coordinate data with a precision sufficient for most craniometric research. Copyright © 2010 John Wiley & Sons, Ltd.     

3D model of the Can Sadurní cave

Graphic and metric information about the site and its environment and about the different structures and artefacts located are indispensable for the optimal management of an archaeological excavation. A Geographic Information System (GIS) proves useful in managing and analysing information and data obtained from different sources. Two techniques of data capture, Terrestrial Laser Scanning (TLS) and close range photogrammetry, are used to generate accurate and high-resolution 3D models of a cave, the silos and a combustion structure at the Can Sadurní site (Begues, NE Spain). This site is especially noteworthy on account of its complete stratigraphy of the Catalonian Holocene. The capture and processing of the photogrammetric and TLS data used to generate 3D models are discussed in detail. These models cannot be obtained by classic archaeological techniques since the record is made layer by layer, approximately one decimetre apart, with the result that the information between the layers is lost. Our findings highlight the potential of these techniques for obtaining accurate and photorealistic models that facilitate a complete analysis of the available information at an archaeological site.     

Statistical Network Analysis for Analyzing Policy Networks

To analyze social network data using standard statistical approaches is to risk incorrect inference. The dependencies among observations implied in a network conceptualization undermine standard assumptions of the usual general linear models. One of the most quickly expanding areas of social and policy network methodology is the development of statistical modeling approaches that can accommodate such dependent data. In this article, we review three network statistical methods commonly used in the current literature: quadratic assignment procedures, exponential random graph models (ERGMs), and stochastic actor‐oriented models. We focus most attention on ERGMs by providing an illustrative example of a model for a strategic information network within a local government. We draw inferences about the structural role played by individuals recognized as key innovators and conclude that such an approach has much to offer in analyzing the policy process.     

关中天水经济区核心—边缘旅游空间结构解析

核心—边缘结构是区域旅游空间结构演化的重要解释模型,本文从复杂系统理论和分形理论切入重新解构旅游空间结构演变特征、动态过程和测度方法。以关天经济区为例实证分析并得出结论:核心—边缘旅游空间结构具有层次性、涌现性和分形的特征,演变过程分为核心集聚极化、边缘扩散溢出和空间动态平衡三个阶段;首位度、分形等方法能很好揭示旅游空间结构演化过程;关天经济区旅游空间属于典型的核心—边缘结构,目前处于核心集聚极化阶段后期,溢出效应逐步显现,次级核心基本形成,空间结构与等级结构紧密耦合,发展态势良好。     

柬埔寨吴哥石窟建筑结构形式及其破坏特征分析

柬埔寨吴哥石窟的文物建筑规模宏大．保存完整,蕴含极高的历史、艺术和科学价值,足著名的世界史化遗产,在世界建筑史上占有重要的地位。本研究从结构工程的角度,介绍了吴哥石窟建筑结构形式．并在现场勘察的基础上简述了吴哥石窟建筑破坏的类型,即结构破坏与材料破坏两种类型,在保护修复中,应针对不同的破坏肜式采取相应的技术措施。     

SIMPLIFIED MODELLING STRATEGIES TO SIMULATE THE DYNAMIC BEHAVIOUR OF R/C WALLS

A continuous damage model and different simplified numerical strategies are proposed to simulate the behaviour of reinforced concrete (R/C) walls subjected to earthquake ground motions. For 2D modelling of R/C walls controlled primarily by bending, an Euler multilayered beam element is adopted. For 3D problems, a multifibre Timoshenko beam element having higher order interpolation functions has been developed. Finally, for walls with a small slenderness ratio we use the Equivalent Reinforced Concrete model. For each case, comparison with experimental results of R/C walls tested on shaking table or reaction wall shows the advantages but also the limitations of the approach.     

NONLINEAR SHAKE TABLE IDENTIFICATION AND CONTROL FOR NEAR-FIELD EARTHQUAKE TESTING

The primary focus of a structural shake table system is the accurate reproduction of acceleration records for testing. However, many systems deliver variable and less than optimal performance, particularly when reproducing large near-field seismic events that require extreme table performance. Improved identification and control methods are developed for large hydraulic servo-actuated shake table systems that can exhibit unacceptable tracking response for large, near-field seismic testing. The research is presented in the context of a 5-tonne shake table facility at the University of Canterbury that is of typical design. The system is identified using a frequency response approach that accounts for the actual magnitudes and frequencies of motion encountered in seismic testing. The models and methods developed are experimentally verified and the impact of different feedback variables such as acceleration, velocity and displacement are examined.

The methods show that shake table control in testing large near-field seismic events is often a trade off between accurate tracking and nonlinear velocity saturation of the hydraulic valves that can result in severe acceleration spikes. Control methods are developed to improve performance and include both acceleration and displacement feedback to reduce the acceleration spikes, and record modification, where the reference signal is modified to conform to the shake table's operational parameters. Results show record modification gives exact tracking for near-field ground motions, and optimal system response for reference signals with velocity components greater then the system capabilities. Overall, the research presents a methodology for simple effective identification, modelling, diagnosis and control of structural shake table systems that can be readily generalised and applied to any similar facility.     

STRUCTURAL RESPONSE AND DAMAGE ASSESSMENT BY ENHANCED UNCOUPLED MODAL RESPONSE HISTORY ANALYSIS

The Uncoupled Modal Response History Analysis (UMRHA) method developed by Chopra et al. is modified in this paper to estimate damage to welded moment-resisting connections in a steel frame (MRSF) subjected to earthquake ground motions. The behaviour of these connections is modelled by a moment-rotation relationship that accounts for the cracking of the beam flange-to-column flange groove weld. The behaviour of the frame is approximated by a sequence of single-degree-of-freedom (SDOF) models for the first three modes to allow for the contribution of higher modes of vibration. The dynamic properties of these SDOF systems are determined by nonlinear static pushover analyses of the building frame. Because of the significant drop in connection strength caused by beam-to-column weld cracking, the pushover procedure uses a changing rather than invariant distribution of horizontal loads, while the structural responses are calculated from shapes that are based on the displaced shape of the frame after damage occurs. The accuracy of the method is demonstrated by a comparison with the results of a nonlinear time history analysis of the frame. This method can be used for rapid assessment of seismic damage or damage potential and to identify buildings requiring more detailed investigation.