年轮, 它们也有

年轮,显示了树木生长的年龄。海洋生物,特别是海洋动物是否也有年轮呢?科学家回答:有……鳞片青鱼、草鱼、鲤鱼、鲢鱼等多数鱼类,可以用鳞片来推算年龄。因为鱼鳞也象树木一样有年轮。这是由于鱼的年龄增长了,鳞片也会随之生长。如果仔细观察,你可以看到在鱼鳞片的上面,有许多同心的环纹。这环纹仿佛树木横断面上的环纹一样,叫做年轮。鱼类的年轮是怎样形成的呢?原来鱼类在春夏时节,食物丰富,生长旺盛,鳞片生长加快,产生很亮很宽的同心圈。同心圈的距离远,叫做夏轮,在秋冬季节,食物较少,生长也就缓慢,鳞片生长也就缓慢,产生很暗很黑的同心圈,圈与圈的距离很近,叫冬轮。

Fiber Bragg Grating Pressure Sensor Based on Corrugated Diaphragm

A kind of fiber Bragg grating pressure sensor based on corrugated diaphragm is proposed. The relationship between the central wavelength of reflective wave of FBG and pressure is given, and the expression of the pressure sensitivity coefficient is also given. Within the range from 0 MPa to 0.3 MPa, the experimental pressure sensitivity is 7.83 nm/MPa, which is 2 610 times than that of the bare fiber grating. The experimental results agree with the theoretical analysis. It is indicated that the expected pressure sensitivity of the sensor can be obtained by optimizing the size and mechanical parameters of the corrugated diaphragm.

母亲的树

母亲一生对树有一份特殊的情感。我的记忆里,母亲年年春天都要植上几棵树,或桑或槐,或柳或梧桐,长满了老家屋后的河堤;桃、梨、杏、柿之类的果树,更是挤满了老家的庭院。有众树陪伴老屋,春天总是过早来到我家。第一阵春风刮过,第一场春雨落下,几乎一夜之间,桑树吐绿、槐树生枝、杨树婆娑、梧桐孕蕾;院中更是枝枝繁花,或粉或红,招蜂引蝶,梨树、杏树。

熟手速成

没有人天生就是熟手。只要依步骤实施,2至14天即可用,3个月至1年即能独当一面,何患新手到处惹祸,大伙儿疲于奔命赶着善后?许多台商老板反映:大陆员工素质差,习惯顽劣,不是短时间能够调教出来的,