首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Imagine an accident in which a nuclear power plant releases radioactive gas. The cloud starts moving with the wind. Clearly, the
Imagine an accident in which a nuclear power plant releases radioactive gas. The cloud starts moving with the wind. Clearly, the
admin
2010-02-21
91
问题
Imagine an accident in which a nuclear power plant releases radioactive gas. The cloud starts moving with the wind. Clearly, the authorities will want to evacuate anyone in its path, but what is that path? Local wind information is meaningless without information about terrain, a mountain range or series of valleys can divert both wind and gas in unpredictable directions.
To make "downwind" a useful term, scientists at Lawrence Livermore National Laboratory have put the United States on a computer, the entire United States-every hill, every valley, every mile of seashore. Within minutes of a disaster, they can give meteorologists a context for weather data, and thus the ability to predict how toxic gases might spread.
The database for this computer map is a series of altitude measurements, made over many years by the Defense Department and the U.S. Geological Survey. They represent the height above sea level of over a billion separate points--a grid of points 200 feet apart, spanning the country. Armed with these data, plus a program that manipulates them, a Cray-1 computer can produce an image of any piece of terrain, seen from any angle, illuminated by an imaginary sun at any time of day placing the "observer" at any altitude from zero to 40,000 feet.
"We use a technique called ray tracing," says Patrick Weidhaas, one of the Livermore computer scientists who wrote the program. The computer is told where the observer is. The program traces an imaginary ray from there outward until it "intersects" with one of the points’ of altitude recorded in the machine’ s memory. The computer then puts a dot of color at the proper place on the screen, and the program traces another ray.
At its highest resolution of 2,000 horizontal and 1,700 vertical dots per picture, the computer has to trace several million rays. Even on the Cray, the most powerful computer in the world, this takes about a minute. Reducing the resolution to 400~300 (a TV screen has 800 x 700) speeds it up to about eight seconds. "We can’t produce a movie simulating flight on the screen in real time," says Weidhaas. There is a way around the problem: Two movies have been made using still pictures generated by the computer as individual frames. "The results were impressive," he says, "but it was cumbersome to do. At twenty-four frames per second, it takes fourteen hundred separate computer images to make a one-minute film." Another limitation. The computer can access only enough memory to cover a 15-mile-square area. An "observer" high up will see blank spaces beyond those limits.
Weidhaas wants to add information about what overlies the terrain-cities, vegetation, roads, and so on. "Making the image as realistic as possible will make our advice more effective," he says, "and might lead to uses we haven’t thought of yet."
The information used by the computer to make its detailed maps ______. Ⅰ. was gathered by the Defense Department and the U. S. Geological Survey Ⅱ. shows points roughly 200 feet apart Ⅲ. involves altitude measurements
选项
A、Ⅰ
B、Ⅰ and Ⅱ
C、Ⅰ and Ⅲ
D、Ⅰ, Ⅱ and Ⅲ
答案
D
解析
第三段说the computer map的database包括altitude measurements,而这些资料又是由the Defense Department and the U.S.Geological Survey搜集的,后文又提到a grid of points 200 feet apart,选项D正确。
转载请注明原文地址:https://kaotiyun.com/show/9vIO777K
0
考博英语
相关试题推荐
NewZealand’shighestearningexportsarePeterBullsaysthattheKMBwassetupinordertoincrease
•Lockatthenotesbelow.•Someinformationismissing.•Youwillhearawomantalkingaboutpersonalexperience.•Foreach
•LookatthenotesaboutanAmericanbusinessmancalmedMatthewWebb,whoisworkingintheUKforacompanycalledElectra.•So
WhichofthefollowingistheresponsibilityofanHRmanager?Internalapplicantsare______betterthanoutsiders.
ENOUGHELECTRICITY
Howmuchdoesthepriceincrease?
QualificationsYoumustpossessaBachelororaMasterofSciencedegreeinComputerScienceorComputerEngineeringwithmoret
CasaltalianaTwentyyearsago,itwasdifficulttofindfreshpastainBritainwithoutgoingtoanItalianrestaurant.
LittletonNewsUpdateTherateofunemploymentinLittleton,asmalltowninthesouthwestofEngland,hasreachedarecord
HowtosetpricesThemethodsadoptedinpricesettingarecrucialtoanybusiness.Whensettingprices,remembercostswill
随机试题
“身联网”是一种以人体为中心并与互联网连接的新兴技术。“身联网”设备是一种人机交互产品与互联网相结合的产物。既包括附着式设备,还包括半植入式与植入式没备。植入式设备是完全植入人类体内的。如果发生非正常断裂,则有可能随血液循环进入心脏、大血管等,进而引发栓塞
在交易过程中,如果交易双方都积极寻求响应,这种情况称为【】
下列有关纤连蛋白的叙述,错误的是
既善行气,又和胃安胎的药物是
患者,男,40岁。乙肝病史10年,近2个月右上腹胀痛加重。检查:面部有蜘蛛痣,右上腹压痛,肝肋缘下3cm,质硬,ALT40U,HBsAg(+),AFP500μg/L。应首先考虑的是
一般资料:求助者,男性,2l岁,高中学历,一年前来城市打工。下面是心理咨询师与求助者的一段咨询对话:心理咨询师:记得你上次临走时说一周之后再来咨询的,现在半年都过去了,你不觉得时间太长了吗?这次又有什么问题需要帮助?是新问题还是老问题?求助者:上次
可导致肾小球滤过率降低的因素是()。
中国人民银行公布的统计数据显示,2007年全国银行卡发卡总量149995.06万张,同比增长32.63%。其中,借记卡140968.78万张,同比增长30.36%;贷记卡7161.53万张,同比增长144.08%;准贷记卡1864.75万张,同比减少7
(2011年真题)下列情形中,收养关系有效的是()。
Wheredidthisconversationprobablytakeplace?
最新回复
(
0
)