如何用英语介绍赵州桥

Zhaozhou Bridge
The Zhaozhou Bridge (traditional Chinese: 赵州桥; simplified Chinese: 赵州桥; pinyin: Zhàozhōu Qiáo) is the worlds oldest open-spandrel stone segmental arch bridge.[1] Credited to a craftsman named Li Chun, the bridge was constructed in the years 595-605 during the Sui Dynasty. Located in the southern part of Hebei Province, it is the oldest standing bridge in China, although the Chinese had built bridges over waterways since the ancient Zhou Dynasty.
Name and location
The Zhaozhou Bridge is also known as the Safe Crossing Bridge (traditional Chinese: 安济桥; simplified Chinese: 安济桥; pinyin: An Ji Qiáo, englished as the Anji Bridge) and the Great Stone Bridge (Chinese: 大石桥; pinyin: Dà Shí Qiáo). It crosses the Xiao River (traditional Chinese: ; simplified Chinese: 洨河; pinyin: Xiào Hé, Jiao He) in Zhao County, approximately 40 km southeast of the provincial capital Shijiazhuang. It is named for the nearby Zhao County (赵县), which was formerly known as Zhaozhou (赵州).
Construction
The Zhaozhou Bridge is about 50 m long with a central span of about 37 m. It stands 7.3 m tall and has a width of 9 m. The arch covers a circular segment less than a semicircle and has a rise-to-span ratio of approximately 1:5 (7.3 to 37 m). This is considerably smaller than the rise-to-span ratio of 1:2 of a semicircular arch bridge and subjects the abutments of the bridge to large forces.
The central arch is made of 28 thin, curved limestone slabs which are joined with iron dovetails. This allows the arch to adjust to shifts in its supports, and prevents the bridge from collapsing even when a segment of the arch breaks. The bridge has two small side arches on either side of the main arch. These side arches serve two important functions: First, they reduce the total weight of the bridge by about 15.3% or approximately 700 tons, which is vital because of the low rise-to-span ratio and the large forces on the abutments it creates. Second, when the bridge is submerged during a flood, they allow water to pass through, thereby reducing the forces on the structure of the bridge.
Li Chuns innovative spandrel-arch construction, while economising in materials, was also of considerable aesthetic merit. An inscription left on the bridge by Tang officials seventy years after its construction reads:
“ This stone bridge over the Jiao River is the result of the work of the Sui engineer Li Chun. Its construction is indeed unusual, and no-one knows on what principle he made it. But let us observe his marvellous use of stone-work. Its convexity is so smooth, and the wedge-shaped stones fit together so perfectly... How lofty is the flying-arch! How large is the opening, yet without piers!.. Precise indeed are the cross-bondings and joints between the stones, masonry blocks delicately interlocking like mill wheels, or like the walls of wells; a hundred forms (organised into) one. And besides the mortar in the crevices there are slender-waisted iron cramps to bind the stones together. The four small arches inserted, on either side two, break the anger of the roaring floods, and protect the bridge mightily. Such a master-work could never have been achieved if this man had not applied his genius to the building of a work which would last for centuries to come.[2] ”
Later history and reputation
In the next 1400 years, the bridge survived at least eight wars, ten major floods and numerous earthquakes, the nearest of which being the 7.2 degree Xingtai Earthquake in 1966. Yet, the support structure remains intact and the bridge is still in use. Only the ornamental railings have been replaced every few hundred years.
The intriguing design of the bridge has given rise to many legends. According to one legend, the bridge was built by a master architect named Lu Ban in a single night. In another story, the bridge was put to the test by two immortals who crossed it at the same time and Lu Ban saved it by wading into the water and supporting the structure.
Although Ming Dynasty authors compared the bridge to "a new moon rising above the clouds" and "a long rainbow hanging on a mountain waterfall"[2], it later fell into obscurity. When Professor Liang Sicheng (梁思成) of Tsing Hua University rediscovered the bridge on a field exploration of ancient architecture in Hebei province, made detailed measurements, and published a report and drawing ("An Chi Chiao the Great Stone Bridge Chao Hsien, Hobei, Sui Dynasty AD 569-617, Li Chun Master Builder"), it became world famous.
Zhaozhou Bridge was dedicated as an International Historic Civil Engineering Landmark by the American Society of Civil Engineers in 1991. The Chinese authorities nominated it for incription on the World Heritage List as having "a very important place in the world bridge building history".[2]
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You can tell your friend to google it online--Zhaozhou Bridge.

怎么在PPT里使用 行云流水 主题

在PPT里使用行云流水主题的具体操作步骤如下：
1、首先在PPT中打开需要进行更换主题的PPT文件，然后点击上方选项卡中的“设计”选项卡。



2、然后点击“设计”选项卡下的“颜色”选项后方的小倒立三角形。



3、然后在“颜色”的下拉选项框中，可看见“行云流水”字样的选项，点击此选项。然后就可以更换完成了。

求微分方程变传递函数，详细过程，感激不尽

以一个二阶线性常微分方程为例说明求传递函数的过程：
系统的输入函数：x(t)；系统的输出函数为：y(t)；对应的微分方程为：
ay +by+cy = px +qx (1)
a,b,c,p,q 均为常数；一撇表一阶导数、两撇表二阶导数。
对微分方程(1)两边作拉氏内变换：
(as²+bs+c)Y(s) = (ps+q)X(s) (2)
其中Y(s)、X(s)分别为输出和输入函数的拉氏变换。
由(2)可以解出(1)的传递函容数：
H(s)＝Y(s)/X(s) = (ps+q)/(as²+bs+c) (3)
即微分方程输出的拉氏变换与输入的拉氏变换之比
即为传递函数。