矢量数据栅格化的一种有效方法——环绕数法

矢量数据栅格化是GIS数据处理的一项重要任务。目前,已存在多种栅格化方法,但是每种方法都有各自的局限性。本文首次提出了环绕数法,它基于计算几何转角理论,通过计算跨越数来确定环绕数,是一种简单、高效、易于实现的栅格化方法。应用环绕数法,不但可以完成简单多边形的栅格化,而且可以完成自交多边形的栅格化。     

萨拉热窝：“欧洲的耶路撒冷”

波斯尼亚和黑塞哥维那共和国,是一个面积只有浙江省一半的欧洲新国家。不过,我乘坐的国际列车从该国北端驶入以后,摇摇晃晃地走了七八个小时,依然没有到达中部的首都萨拉热窝。铁路两侧尽是低矮的山谷和溪流,间或可见清真寺的尖塔露出村头,黄色的砖墙被绿色的庄稼和杂乱的树木环绕着。车上旅客稀少,仅有的几位也因为语言不通而无法交流。黄昏时分,     

小地图，大文章——地图上争议岛屿的表示

岛屿是海洋里被水环绕、面积比大陆小的陆地,也指湖里、江河里被水环绕的陆地。本文所谈的岛屿,主要是指海洋中的岛屿。人们通常把岛屿比喻为散落在海洋里的珍珠,它们不仅美,很多还具有重要的政治、军事、经济等战略价值。     

世界梯田之冠——金坑梯田

据资料记载,金坑梯田已有600多年历史,始建于元朝,完工于清初。金坑梯田似一条条巨龙环绕在一座座山峰上。清晨或旁晚,时常出现"火烧云"或形成云雾景观。从不同的角度看去,金坑处处是美丽的"画廊"。     

流浪行星的故事

行星应该环绕恒星运转,这是天文学上再简单不过的常识。从天体演化的角度看,现在也一般认为是先形成中央的恒星,然后星周盘的物质再凝聚成行星,因此这条常识也是很自然的推论。在这样的背景下,无依无靠、没有主恒星的流浪行星乍看之下就显得很古怪了。     

全景式俯瞰环绕俄罗斯的雪白色飘带叶尼塞河

屈指可数世界第五大长河全长5539公里 无与伦比流入北冰洋最大河流 黄金水道该河有3013公里可定期通航     

The Circum-Pacific Teleconnection Pattern in meridional wind in the high troposphere

The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR reanalysis data. The CPTP is found to be composed of the North Pacific-North American teleconnection pattern (PNA), the South Pacific-South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.     

沈阳在历史七彩环绕中更加扮靓其地名光彩

“沈阳”一名源于元成宗元贞二年（1296年）设置的沈阳路。因地处沈水（今浑河）之北（“水北为阳”）得名。春秋战国时期,沈阳成为燕国的属地,为肃慎氏所有。燕昭王十二年（公元前300年）,燕国在此屯兵戍边,设立候城,为沈阳建城之始。秦代,沈阳属辽东郡境。西汉时,沈阳为中部都尉治所,已初具县邑规模。     

Extinction of Beamed Gamma-ray Burst Afterglows in a Dense Circumstellar Cloud

Broadband afterglow observations provide a probe of the density structure of the circumburst medium. In the spreading jet model, prompt and intense X-ray/UV radiation from the reverse shock may destroy and clear the dust in the circumburst cloud out to about 30 pc within the initial solid angle of the jet. Asthe jet expands significantly, optical radiation from the high-latitude part of the jet may suffer extinction by dust outside the initial solid angle, while radiation from the part within the initial solid angle can be observed without extinction. In previous studies, it is usually assumed that the extinction is complete. We calculate the extinction effect by taking the optical depth into account. Our numerical results showthat a break appears in the light curve of optical afterglow but it extends over a factor of ～ 80 in time rather than a factor of ～ 10 in time for the case of strong dust extinction and a factor of ～ 60 in time for the case without dust extinction. These results may provide a way to judge how large the number density of the circumburst cloud is. Finally, we carry out a detailed modeling for the afterglow of GRB 000926. Our model can provide a good fit to the multi-color observations of this event.