何谓“P”坐标系?及其优缺点?
已知局地直角坐标系其坐标轴采用(x,y,z),其中的垂直坐标以几何高度z来表示,故也称它为”z”坐标系。由于大气的垂直高度与气压有很好的静力学关系,可用气压p来表示垂直坐标,即空间点的位臵用(x,y,p)坐标来表示,这种坐标系称为“P”坐标系。
它有很多优点:气象上用的天气图,除地面图外,高空图都是等压面图,即是一种“P”坐标图,由于等压面相对水平面的坡度很小,因此它又具有准水平面的特点。在“P”坐标系中,通过静力学关系,可得到用等压面上的位势高度场特征来表示气压场的特征,气压梯度力成为线性项,形式简单。此外,运动方程组可少了密度这个变量,连续方程也变的较为简单,p坐标系用于研究大尺度运动较为合适。
其缺点是:由于采用了静力学近似关系,所以p坐标系运动方程组不能用于研究存在非静力平衡的运动现象,如某些小尺度运动。此外,p坐标系的缺点是难以正确地给出下边界条件。
Project selection methods involve measuring value or attractiveness to the project owner or sponsor and may include other organizational decision criteria ()is not a project selection method.
() are individuals and organizations that are actively involved in the project, or whose interests may be affected as a result of project execution or project completion.
() are individuals and organizations that are actively involved in the project, or whose interests may be affected as a result of project execution or project completion.
No more having to buy expensive textbooks which you will only use for a year or two and then sell or _______ away.
达成协议有许多种方式,方式及其优缺点对应正确的是( )。
Goods are carried by several of transport--on road or rail, by sea or air.
You can _____ some bottles of wine, or some chocolates, or a bunch of flowers.
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
_____she comes or not makes no difference.
2002年新配方口服补液盐(ORS)溶液的张力是
达成协议有许多种方式,方式及其优缺点对应正确的是( )。
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