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91.
Kai Kang 《Fire Technology》2007,43(4):331-346
This paper presents an emergency evacuation analysis during a mid-platform train fire in an underground rail station. A time-based
evacuation scenario is developed taking into account the stairway inaccessibility due to smoke blockage. The calculation approach
in NFPA 130 is then applied to a parametric study of this time-based scenario and its reliability is examined using a micro-simulation
model. Both methods give consistent predictions of the exiting times. The results demonstrate that with the division of the
station into two zones, the exiting time could not meet the code requirements, whereas it does meet the required exiting time
without the division. Such division is due to smoke blockage and creates an uneven ratio of the occupant load to the available
exiting capacity. This shows that appropriate consideration of the fire and smoke effects is important for station egress
evaluation. Other issues such as the fire growth rate and the pre-evacuation time are also discussed. 相似文献
92.
We use accelerated molecular dynamics to probe the thermal desorption of n-alkanes from the Au(1 1 1) and C(0 0 0 1) surfaces. Studying an alkane series ranging from CH4 to C16H34, we find that the desorption prefactor increases with increasing chain length for the short chains until a certain chain length is reached when it becomes essentially constant and independent of chain length. We can understand the dependence of the preexponential factor on alkane chain length in terms of conformational changes within the alkane molecules. For the shorter molecules, the desorption temperatures probed in experimental temperature-programmed desorption studies lie below those for which torsional motion is activated. Thus, the short alkanes can be treated as rigid rods, and the loss in translational and rotational entropy upon adsorption leads to a preexponential factor that increases with increasing chain length. As the alkane chain length increases, the binding energy and the experimental desorption temperatures also increase. Thus, torsional motion is activated to an extent that increases with increasing chain length. This torsional activation increases the entropy of adsorption and counteracts the entropy decrease due to a loss of translation and rotation. This leads to a virtually constant prefactor for sufficiently long chains. Our findings are consistent with experimental data for the thermal desorption of alkanes from the Au(1 1 1), Pt(1 1 1), MgO(1 0 0) and C(0 0 0 1) surfaces. 相似文献
93.
94.
Yu Yang Hugo Bender Kai Arstila Bart Swinnen Bert Verlinden Ingrid De Wolf 《Microelectronics Reliability》2008,48(8-9):1517-1520
Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination. 相似文献
95.
WANG Kai WANG Bei WU Rui-zhi 《国际设备工程与管理》2007,12(3):154-159
In order to reduce the vibration on a machine tool, more orthogonal experiment schemes have been designed, which are based on the steel balls vibration reducing principle. After experiments the optimal reducing vibration scheme was determined. This kind of vibration reducing scheme is used in steel balls vibration absorber, which can be used to reduce vibration magnitudes of a machine tools under the working conditions, whereby improving machining precision. The suggested experiment method is of useful reference in reducing vibrations on other machine tools too. 相似文献
96.
97.
The development of autonomous mobile machines to perform useful tasks in real work environments is currently being impeded
by concerns over effectiveness, commercial viability and, above all, safety. This paper introduces a case study of a robotic
excavator to explore a series of issues around system development, navigation in unstructured environments, autonomous decision
making and changing the behaviour of autonomous machines to suit the prevailing demands of users. The adoption of the Real-Time
Control Systems (RCS) architecture (Albus, 1991) is proposed as a universal framework for the development of intelligent systems. In addition it is explained how the use
of Partially Observable Markov Decision Processes (POMDP) (Kaelbling et al., 1998) can form the basis of decision making in the face of uncertainty and how the technique can be effectively incorporated into
the RCS architecture. Particular emphasis is placed on ensuring that the resulting behaviour is both task effective and adequately
safe, and it is recognised that these two objectives may be in opposition and that the desired relative balance between them
may change. The concept of an autonomous system having “values” is introduced through the use of utility theory. Limited simulation
results of experiments are reported which demonstrate that these techniques can create intelligent systems capable of modifying
their behaviour to exhibit either ‘safety conscious’ or ‘task achieving’ personalities. 相似文献
98.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献
99.
One of the most frequently cited reasons for conducting a meta-analysis is the increase in statistical power that it affords a reviewer. This article demonstrates that fixed-effects meta-analysis increases statistical power by reducing the standard error of the weighted average effect size (T?.) and, in so doing, shrinks the confidence interval around T?.. Small confidence intervals make it more likely for reviewers to detect nonzero population effects, thereby increasing statistical power. Smaller confidence intervals also represent increased precision of the estimated population effect size. Computational examples are provided for 3 effect-size indices: d (standardized mean difference), Pearson's r, and odds ratios. Random-effects meta-analyses also may show increased statistical power and a smaller standard error of the weighted average effect size. However, the authors demonstrate that increasing the number of studies in a random-effects meta-analysis does not always increase statistical power. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
100.