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Quantum mechanic computer models are often used in chemistry to predict properties of molecules and to simulate reaction pathways. Such models calculate bond lengths, bond angles, dihedral angles, the energy of the molecular‐orbitals (MO's), the dipole moment, the ionisation potential, and the heat of formation. These results lead to detailed information on electronic structures like bond orders, electronic charges and levels of frontier orbitals (HOMO, LUMO). It is possible to calculate properties of ground state molecules as well as ionic and radicalic structures, or reaction intermediates and other compounds with very short lifetimes. From the exact knowledge of electronic structure, frontier orbitals, and reaction intermediates it is possible to predict stability of chemicals in the environment but also of fictive chemicals, which are not yet synthesized. Some authors have shown that there are correlations between electronic structure and toxicity. The most interesting models for environmental chemistry are semiempirical models, such as MINDO, MNDO or MOPAC. Theses programs are able to handle molecules with 30 and more heavy atoms (all elements without hydrogen), and it is possible to install them on main frame computers (CPU‐time several minutes to hours) and on personal computers, with coprocessors (CPU‐time several hours to a few days). Normally the molecule is read in from a Z‐matrix (a matrix of polar coordinates of atoms connected in the molecule) and with symmetry data. Furthermore, programs are available which create a Z‐matrix from the molecular structure plotted on the screen with a mouse. 相似文献
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利用RADARSAT SWA SAR和LANDSAT TM的互补信息确定洪水水体范围 总被引:7,自引:0,他引:7
从RADARSAT SAR图像中自动提取洪水水体,一直是一个急需解决而又未能得到解决的问题。主要困难是由于阴影与水体严重相混淆。为此,本文研究发现,通过RADARSAT SWA SAR图像和LANDSAT TM图像上的互补信息,利用RADARSAT SWA SAR图像和LANDSAT TM图像上的水体和阴影进行复合处理,可以从RADARSAT SWA SAR图像上准确、半自动提取洪水水体范围。研究结果表明,该方法不仅适用于平地洪水水体范围的半自动提取,而且更适用于包含山区的大范围洪水水体的半自动提取。 相似文献
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中国省域尺度下产业结构多维度特征及演化对碳排放的影响 总被引:1,自引:0,他引:1
在中国转向高质量发展及2030年前达到碳排放峰值的背景下,寻找保证经济增长的低碳减排途径是学界研究的热点。利用中国2005—2017年省域面板数据,建立SAR模型,并按八大经济区分别构建PECM模型,研究中国省域尺度下产业结构多维度特征及演化对碳排放的影响,主要结论如下:(1)中国省域碳排放具有显著的时滞性和空间溢出效应。(2)全国视角下,产业结构合理化水平提升对碳排放呈抑制作用,且存在负向空间溢出效应;而产业结构高度化对碳排放呈促进作用,且存在正向空间溢出效应,总体上处于“倒U型”曲线左侧。(3)八大经济区视角下,随着经济发展水平的提高,产业结构合理化水平提升总体上能够抑制碳排放,而产业结构高度化水平提升则呈现明显的“倒U型”趋势特征,具有两面性,发达地区呈现抑制效应,欠发达地区则相反;当前处于“倒U型”曲线右侧的区域多为发达地区。因此,由产业结构高度化提升导致碳排放量的增加依然属于中国多数省份当前发展的固有阶段性特征,而产业结构合理化提升在总体上能够拉动碳排放峰值前移,促使碳排放早日达峰。欠发达地区不应以增大三产份额为目标,盲目推动产业结构高度化水平提升,这将很有可能对区域经济发展产生负面影响;而产业结构合理化水平提升是既能够适应中国多数省份当前发展惯性,同时又能促进减排或排放降速的有效途径。 相似文献
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Hubert Trzaska 《The Environmentalist》2005,25(2-4):181-185
Summary The paper discusses several aspects of the practical application of the SAR. It is shown that the unit is an ideal solution
for basic research and laboratory experiments. SAR is directly nonmeasurable unit. Although methods and devices based upon
indirect SAR measurements may widen our knowledge about EM energy distribution and absorption within a body. It is shown that
for practical applications the temperature SAR measurement methods are not sensitive enough while methods based upon E(H) measurement are less accurate than traditional approaches. As a result of assumption SAR = 4 W/kg as a basic restriction
the present protection standards are illogical and nonrealiazable. A return to traditional units (E, H, S) in the standards
and surveying metrology is suggested. 相似文献