An improved hypoplastic constitutive model of rockfill considering effect of stress path

An incrementally nonlinear hypoplastic constitutive model was introduced, which was developed without recourse to the concepts in elastoplasticity theory such as yield surface, plastic potential and the decomposition of the deformation into elastic and plastic parts. Triaxial drained tests on rockfill were conducted on a large scale triaxial apparatus under two types of stress paths, which were the stress paths of constant stress ratio and the complex stress paths with transitional features. Motivated by the effect of stress path, the Gudehus-Bauer hypoplastic model was improved by considering the parameter variations with different ratios of stress increment. Fitting parameter a presents a piecewise linear relationship with cosine of the slope angle θ determined by instantaneous stress path. The improved hypoplastic model can present peak stress increasing and volumetric strain changing from dilatancy to contractancy with the increase of transitional confining pressure σ3t and the decrease of slope angle θ of stress path. Compared with the test data, it is shown that the model is capable of fully considering the effect of stress path on rockfill.

Posterior Selective Thoracic Fusion in Adolescent Idiopathic Scoliosis Patients:a Comparison of All Pedicle Screws versus Hybrid Instrumentation

Objective To analyze the influence of segmental pedicle screws versus hybrid instrumentation on the correction results in adolescent idiopathic scoliosis patients undergoing posterior selective thoracic fusion. Methods By reviewing the medical records and roentgenograms of adolescent idiopathic scoliosis patients who underwent selective thoracic fusion from February 2000 to January 2007 in our hospital, the patients were divided into 2 groups according to different instrumentation fashions： Group A was hook-screw-rod （hybrid） internal fixation type, Group B was screw-rod （all pedicle screws） internal fixation type, and the screws were used in every segment on the concave side of the thoracic curve. The parameters of the scoliosis were measured and the correction results were analyzed. Results Totally, 48 patients （7 males, 41 females） were included, with an average age of 14.4 years old and a mean follow-up time of 12.3 months. Thirty and 18 patients were assigned to group A and group B, respectively. The mean preoperative coronal Cobb angles of the thoracic curve were 48.8° and 47.4°, respectively. After surgery, they were corrected to 13.7° and 6.8°, respectively. At final follow-up, they were 17.0° and 9.5°, with an average correction rate of 64.6% and 79.0%, respectively, and the correction rate of group B was significantly higher than that of group A （P=0.003）. The mean preoperative coronal Cobb angles of the lumbar curve were 32.6° and 35.2°, respectively. After surgery, they were corrected to 8.6° and 8.3°, respectively. At final follow-up, they were 10.3° and 11.1°, with an average correction rate of 66.8% and 69.9%, respectively, and the correction rate of group B was significantly higher than that of group A （P=0.003）. The correction loss of the thoracic curve and lumbar curve in the 2 groups were 3.1° and 1.8°, 2.4° and 2.4°, respectively. No significant difference was noted （both P〉0.05）. The decompensation rate at final follow-up in these 2 groups were 4% （1/25） and 7.1% （1/14） respectively, with no significant difference （P〉0.05）.

Use of Blackboard Collaborate at Qassim University： Evaluating Teachers＇ Perceptions

Learning has come a long way from the conventional blackboard that marked the earlier decades to the new age Blackboard Collaborate which enables learners to work and learn in a collaborative online environment. Virtual classrooms, especially with learners sharing in academic workload on portals such as Google Docs, have arrived as a natural development of the ICT （In Circuit Tester） wave. In addition to offering ample scope for peer interaction, Blackboard Collaborate gives learners the electronic environment they are most familiar with and keeps them updated with the latest educational tools. However, for it to succeed, the perception of the teachers is a factor that needs close scrutiny before this tool can be incorporated into the system. The aim of this paper is to investigate the perceptions of teachers at Qassim University, KSA （Kingdom of Saudi Arabia） towards the inclusion of Blackboard Collaborate into the teaching-learning environment, and its efficacy as a learning tool in the university＇s EFL （English as a Foreign Language） situation.

A novel wide-range precision instrument for measuring three-dimensional surface topography

We developed a measuring instrument that had wide range, high precision, small measuring touch force. The instrument for three-dimensional (3D) surface topography measurement was composed of a high precision displacement sensor based on the Michelson interference principle, a 3D platform based on vertical scanning, a measuring and control circuit, and an industrial control computer. It was a closed loop control system, which changed the traditional moving stylus scanning style into a moving platform scanning style. When the workpiece was measured, the lever of the displacement sensor returned to the balanced position in every sample interval according to the zero offset of the displacement sensor. The non-linear error caused by the rotation of the lever was, therefore, very small even if the measuring range was wide. The instrument can measure the roughness and the profile size of a curved surface.

Automatic Road Extraction in Rural Areas Based on Digital Imaging and Laser Scanner Data

Digitizing road maps manually is an expensive and time-consuming task. Several methods that intend to develop fully or semi-automated systems have been proposed. In this work we introduce a method, based on the Radon transform and optimal algorithms, which extracts automatically roads on images of rural areas, images that were acquired by digital cameras and airborne laser scanners. The proposed method detects linear segments iteratively and starting from this it generates the centerlines of the roads. The method is based on an objective function which depends on three parameters related to the correlation between the cross-sections, spectral similarity and directions of the segments. Different tests were performed using aerial photos, Ikonos images and laser scanner data of an area located in the state of Parana （Brazil） and their results are presented and discussed. The quality of the detection of the roads centerlines was computed using several indexes - completeness, correctness and RMS. The values obtained reveal the good performance of the proposed methodology.

Laboratory Evaluation of the Stiffness Modulus of a Modified Bituminous Concrete with PR PLAST Sahara

Uneven roads surface can be observed on bituminous pavements. This is due to moving loads and climate conditions. If the observed deformations exceed the elastic limit, important damages can occur, so new materials are used to improve the stiffness modulus of bituminous mixtures. To achieve this, a modified bituminous concrete by addition of the PR PLAST Sahara （produced by PR industries and PLAST for Plastic） mainly used in arid region has been studied. The use of this additive at various percentages 0.1, 0.3, 0.6 and 0.9 by weight of bituminous concrete has been investigated to determine its stiffness modulus. An experimental design using the Taguchi tables has been elaborated to reduce the number of tests. Marshall and NAT （Nottingham asphalt tester） tests have been carried out, and a mathematical model of the stiffness modulus has been proposed.

Commemorative Sculpture and Ceremonial Behaviors in the Public Sphere： Cyprus as a Case Study

This paper focuses on the symbolic power exercised through the memorials in the Republic of Cyprus. Public sculpture is almost exclusively memorial sculpture and it reflects the predominant values of the national identity. This paper constitutes the first analysis of current historical and cultural perceptions in the southern part of the island through these visual representations and the ceremonial behaviors they generate. Characteristic cases of memorials presented here prove that commemoration in the Republic of Cyprus is inextricably linked to location which is either associated with an actual event of death, or draws power from its relation to culturally symbolic institutional buildings. The memorials illustrate the blending of private and public sphere and, respectively, private and social identity of the deceased. They prove that the affinities between heroism and sanctity within the Greek cultural milieu have imbued the social subconscious and impacted significantly on the collective recollections and the national narratives. This paper focuses on the aesthetics of the memorials which, due to their affinities with tombs in Greek and Cypriot cemeteries, lack affirmative hope, healing and closure of the trauma. On the contrary, they persist in portraying victimhood as a state of being.

Simulation of Dynamic Electromagnetic Interference Environment for Unmanned Aerial Vehicle Data Link

In order to test the anti-interference ability of an Unmanned Aerial Vehicle(UAV) data link in a complex electromagnetic environment,a method for simulating the dynamic electromagnetic interference of an indoor wireless environment is proposed.This method can estimate the relational degree between the actual face of an UAV data link in an interface environment and the simulation scenarios in an anechoic chamber by using the Grey Relational Analysis(GRA) theory.The dynamic drive of the microwave instrument produces a real-time corresponding interference signal and realises scene mapping.The experimental results show that the maximal correlation between the interference signal in the real scene and the angular domain of the radiation antenna in the anechoic chamber is 0.959 3.Further,the relational degree of the Signal-toInterference Ratio(SIR) of the UAV at its reception terminal indoors and in the anechoic chamber is 0.996 8,and the time of instrument drive is only approximately 10 μs.All of the above illustrates that this method can achieve a simulation close to a real field dynamic electromagnetic interference signal of an indoor UAV data link.

Parameter Test of ROIC for IRFPA Based on Virtual Instrument Technology

The readout integrated circuit (ROIC) technology is one of the critical technologies in the research of an infrared focal plane array (IRFPA). Based on the virtual instrument technology, a system for parameter test of ROIC is developed for IRFPA. The complex programmable logic device (CPLD) is applied into the system to increase its flexibility. With high reliability and precision, along with the integrated software and hardware environment, the system can test all kinds of ROICs.

意外

仪仪夜色,仪悄无声息仪地笼罩仪了整座仪小镇。仪许是下雪的缘故,此时的小镇比往时更加寂然仪冷清仪,甚至仪让人从心底生出丝丝寒意。小镇里唯一一条仪压过沥仪青的路仪上,偶仪有仪一两辆电动三轮车驶过,'突突——'的声音增仪添了小仪镇的寂寞仪、惆怅仪之感。

Phase control of ellipsometric interferometer for nanometric positioning system

Development in industry is asking for improved resolution and higher accuracy in dimensional metrology. In this paper,we proposed a control displacement method based on a polarization ellipsometirc interferometer and phase-locked loop technique. The proposed principle was set up. The experimental results of step and step displacements with a step value of 5 nm were presented. We also analyzed the resolution,the potential minimal displacement of the established system. The results show that the position error induced by the ellipticty deviation of the light beam becomes negligible thanks to our signal processing circuit with high-order filter. This method could be useful for many applications in nano dimensional metrology and semiconductor industry.