梁柱全焊接节点火灾响应特性分析

采用有限元法对梁柱全焊接节点在火灾下的热、结构响应进行模拟,分析了不同升温条件下全焊接节点的火灾行为,揭示了特定参数对全焊接节点的火灾响应特性,对比分析了全焊连接和栓焊连接节点的抗火性能。结果表明:具有不同升温速率的火灾曲线对全焊节点到达极限状态的时间有显著影响;全焊接节点加载的荷载比越大,节点到达极限状态的时间越短;带有加劲肋的全焊节点耐火时间略长于无加劲肋的节点;在相同升温条件下,全焊节点的耐火时间比栓焊节点的长,抗火临界温度略高于栓焊节点。可为钢结构全焊接节点的抗火设计提供技术参考。     

基于煤矿安全风险成因的国家应对体系研究

基于煤矿安全的重要性,介绍了导致我国煤矿矿难的6大主要风险因素:社会经济发展阶段、煤矿安全生产相关立法情况、能耗结构、煤矿行业人员能力、煤矿技术设备先进程度和监管有效性水平。针对这6个要素,通过问卷调查、深度访谈、案例研究的方式,研究了国家应对煤矿安全风险的体系规划。结果表明:国家在应对煤矿安全风险方面,必须采取5方面的措施,包括制定抑制经济过快增长的宏观政策和鼓励新能源政策、加强立法、吸引煤炭高等院校人才和培训在职人员﹑投资煤炭新技术研究和增加设备投入以及完备有效监管途径。应对体系从宏观、中观和微观的角度提出国家、行业、企业防范煤矿安全风险所要采取的措施,构建了从上而下的提升途径。     

Mitigating construction safety risks using prevention through design

Introduction

Research and practice have demonstrated that decisions made prior to work at construction sites can influence construction worker safety. However, it has also been argued that most architects and design engineers possess neither the knowledge of construction safety nor the knowledge of construction processes necessary to effectively perform Construction Hazards Prevention through Design (CHPtD).

Method

This paper introduces a quantitative methodology that supports designers by providing a way to evaluate the safety-related performance of residential construction designs using a risk analysis-based approach. The methodology compares the overall safety risk level of various construction designs and ranks the significance of the various safety risks of each of these designs. The methodology also compares the absolute importance of a particular safety risk in various construction designs.

Results

Because the methodology identifies the relevance of each safety risk at a particular site prior to the construction stage, significant risks are highlighted in advance. Thus, a range of measures for mitigating safety risks can then be implemented during on-site construction.

Impact on industry

The methodology is specially worthwhile for designers, who can compare construction techniques and systems during the design phase and determine the corresponding level of safety risk without their creative talents being restricted. By using this methodology, construction companies can improve their on-site safety performance.     

Time discounting and the decision to protect areas that are near and threatened or remote and cheap to acquire

Should conservation organizations focus on protecting habitats that are at imminent risk of being converted but are expensive or more remote areas that are less immediately threatened but where a large amount of land can be set aside? Variants of this trade‐off commonly arise in spatial planning. I used models of land‐use change near a deforestation frontier to examine this trade‐off. The optimal choice of where to protect was determined by how decisions taken today accounted for ecological benefits and economic costs of conservation actions that would occur sometime in the future. I used an ecological and economic discount rate to weight these benefits and costs. A large economic discount rate favored protecting more remote areas, whereas a large, positive ecological discount rate favored protecting habitat near the current deforestation frontier. The decision over where to protect was also affected by the influence economic factors had on landowners' decisions, the rate of technological change, and ecological heterogeneity of the landscape. How benefits and costs through time are accounted for warrants careful consideration when specifying conservation objectives. It may provide a niche axis along which conservation organizations differentiate themselves when competing for donor funding or other support.     

On Characteristics of Production and Destruction Processes in Lowland and Mountain Tundras of the Extreme North

Parameters of the production and destruction processes in different types of tundras are compared. It is shown that there is a fairly high degree of correspondence between the structure of tundra communities and the ecotopes occupied by them. On the other hand, typologically similar lowland and mountain tundras markedly differ in the functional respect. The rate of decomposition processes is higher under environmental conditions of the mountain tundra belt.     

Study of high-frequency electromagnetic field effect on some somatic and neuro-behavioral characteristics in healthy and neurodefective mice

The effect of long-term exposure to high frequency electromagnetic field (HF EMF) on some somatic and neural characteristics was studied in neurodefective Lurcher mutant (+/Lc) and normal wild type mice (+/+). Both newborn and young adult (3 months) animals derived from two strains (C3H, B6CBA) were exposed to HF EMF (870 MHz) from 1st to 21st day or from 91st to 120th day respectively. In animals of both groups and controls we observed the development of body weight. Moreover, in the HF EMF exposed adult B6CBA animals we studied spatial learning ability, motor functions and the CNS excitability. To investigate specific energy absorption rate (SAR) in experimental animals we have done the basic 3D calculations of the electromagnetic energy distribution in the simplified model of the mouse. The HF EMF exposed animals exhibited mild differences of body weight between them and unexposed controls. The long-term exposure to HF EMF did not significantly influence the ability to learn in the Morris water maze. However, significant lower swimming speed was found in the irradiated +/Lc as well as lower motor activity of +/+ in the open field when compared to controls. No significant differences were found between HF EMF irradiated animals and controls in examination of the CNS excitability and motor functions.     

Modification of Evacuation Time Computational Model for Stadium Crowd Risk Analysis

The complexity of the evacuation process is associated with the flow of occupants through various egresses available inside the building. Several methods and algorithms are now available to analyse the problem related to evacuation. In the present paper an algorithm, evacuation discrete time model (EDTM) has been presented to analyse the building egress evacuation time problem with previous works. The algorithm is based on the crowd flow theory and uses discrete computational approach to identify various widths of egresses available for movement of the people, which is more accurate and practicable because the crowd flow rate is variable. The developed model has been compared with an existing model to show the capabilities of the developed algorithm. A case of stadium stand egress is chose for the validity of EDTM, and a comparison of EDTM, previous model and computer simulation indicates that both the EDTM and the simulation curves were found to give better predictions than the previous model. Based upon the comparison analysis with stranded crowd and evacuation crowd at a certain time, EDTM shows great value in explaining the cause of stampede-trampling and crushing incident of egress or narrow passage zone.     

Sedimentary Processes of the Qingdao Nearshore Traced Using a Multi-radionuclide Approach

Sediment cores were collected from two sites (A2 and ZQ) in the Qingdao sea area of the Yellow Sea. Radionuclides ⁴⁰K, ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra, ²²⁸Ra, ²²⁸Th, ²³⁴Th, and ²³⁸U in the cores were measured using HPGe γ spectrometry. The sedimentation rate of the A2 Core using ²¹⁰Pb_ex and ¹³⁷Cs was 0.665 cm yr⁻¹, therefore this 32 cm long core represents a 48 year timespan leading to the sampling date in 2001. The mixing layer was restricted to the upper 5 cm as determined from the profile of ²³⁴Th. The uniformity of the activity distributions of ⁴⁰K and ²³⁸U throughout the A2 Core and the activity distributions of ²²⁶Ra, ²²⁸Ra and ²²⁸Th below the mixing layer suggested that no significant oceanographic event or change in sediment material source had occurred during this timespan. The ²¹⁰ Pb was in excess relative to ²²⁶Ra, but ²²⁶Ra was deficient with respect to ²³⁸U in the entire A2 Core, while excess ²³⁴Th and ²²⁸Th were apparent only in the surface 5 cm. Total organic matter (TOM) in Core A2 decreases with depth. The second core, taken to a depth of 14 cm, was from Site ZQ, which is located near Zhanqiao, Qingdao. The variations of the nuclide activity ratios in this core were similar to those in the A2 Core, i.e., the excess ²¹⁰ Pb and ²²⁶Ra deficiency were consistent throughout the core but excess ²²⁸Th was only in the surface to a depth of 2 cm. The ⁴⁰K activity in the ZQ Core fluctuated and showed no real trend with depth. The activities of ¹³⁷Cs, ²¹⁰Pb, ²²⁶Ra and ²³⁸U in the entire length of Core ZQ, and ²²⁸Ra and ²²⁸Th from 2 cm to the bottom, were comparable within the uncertainty of measured activity.