恐龙之死悬而未决

80年代初,加州大学地质学家阿尔瓦雷斯为解释恐龙的灭绝,首先提出一项至今仍广为接受的理论,认为6500万年前,地球曾与一颗巨大陨石相撞,当时遍地漫游的恐龙在这场空前的大浩劫中先后死亡,以至完全绝迹。

Microscopic dynamic simulation model for pedestrian at signalized intersection

Pedestrian's road-crossing model is the key part of micro-simulation for mixed traffic at signalized intersection.To reproduce the crossing behavior of pedestrians,the microscopic behaviors of the pedestrians passing through the crosswalk at signalized intersection were analyzed.A pedestrian's decision making model based on gap acceptance theory was proposed.Based on the field data at three typical intersections in Beijing,China,the critical gaps and lags of pedestrians were calibrated.In addition,considering pedestrian's required space,a modification of the social force model that consists of a self-deceleration mechanism prevents a simulated pedestrian from continuously pushing over other pedestrians,making the simulation more realistic.After the simple change,the modified social force model is able to reproduce the fundamental diagram of pedestrian flows for densities less than 3.5 m-2 as reported in the literature.

浮漂灵敏及迟钝区域的划分新解

二、上迟钝的区域及其应用 以前我们所接受的理论认为浮漂调得越高越灵敏。但文章的前段亦提到另一位学员B浮漂有信号但扬竿中鱼率低的现象,原因是他使用的浮漂是浮力大、漂尾短的空心尾浮漂。要知道一支长20厘米的硬漂尾,同一支长10厘米的空心浮漂相比,未计算漂尾重量时它的浮力一样的话,如果装上漂尾之后,两个都是调三目,后者的三目剩余浮力足足比前者大1～2倍。很明显空心尾调三目的浮漂因为浮力过大,令鱼饵有点离底,鱼饵在池底就很容易前后摆动,鱼儿不能准确地吸食鱼饵,越吸食越急躁,造成很多假动作的出现,亦即形成了另一个“上迟钝”、“假灵敏”的现象。我们研究浮漂时一定要弄清楚,鱼吸食鱼饵的力度一定要大于浮漂的剩余浮力。