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
136
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."
Information about cities, vegetation, and road overlying the terrain ______.
选项
A、has to be eliminated before correct readings can be obtained
B、would be impossible to convert to data that a computer would accept
C、might lead to new applications and improve effectiveness of present uses
D、would make ray tracing obsolete
答案
C
解析
最后一段Weidhaas提出想在地图上增加cities,vegetation,and road是为了使图像尽量逼真make our advice more effective,这也可能lead to uses we haven’t thought of yet,选项C正确。
转载请注明原文地址:https://kaotiyun.com/show/6vIO777K
0
考博英语
相关试题推荐
Lookatthepassagebelow.Someinformationismissing.Youwillhearawomantalkingaboutshoesprices.Foreachquestion9-15
Lookatthenotesbelow.Someinformationismissing.YouwillhearamangivingapresentationaboutArlingtonPark,atraining
Youwillhearalongdialogueonstafftrainingandrecruitingextrastaff.Foreachquestion(23-30),markoneletter(A,BorC)
AssistantToPublicRelationsManagerBusinessPressistheworld’smostrespectedpublisherofbusinessnews.PRandpubli
AssistantToPublicRelationsManagerBusinessPressistheworld’smostrespectedpublisherofbusinessnews.PRandpubli
Launchschedule24/5-Pressconference.31/5-TVadvertisingstarts.Distributeposters.7/6-Deliverleaflets.Radi
语言时空论是语言学这门科学的一个观点。它以时空差异关注语言的流变现象,因为语言的流变基本上是由时间和空间延展在强度和性质上的差异表现出来的。它寻求以客观和精确的方式来描写和揭示语言的基本概念、内在关系以及流变机理,追索有关语言的现实知识。它观察语言流变的原
Yesterdayyouwereacclaimed;todayyouare______.Isn’tlifefullofupsanddowns?
RussianwomenhadtowearprotectivemasksastheywalkedinMoscow,whichwas______byaheavysmogyesterday.
随机试题
B公司2013年1月1日发行三年期.每年1月1日付息、到期一次还本的可转换公司债券,面值总额为10000万元,实际收款10200万元,票面年利率为4%,实际利率为6%。假定债券包含的负债成分的公允价值为9465.40万元,2013年1月1日C公司以4732
小腿后群肌分浅、深两层。()
对便秘患者进行健康指导时,下列哪种做法不妥()。
甲乙之间的合同纠纷经仲裁委员会仲裁,作出裁决。甲认为该裁决对方当事人隐瞒了足以影响公正裁决的证据,向人民法院提出撤销仲裁裁决的申请。以下说法不正确的有:
既有线桥涵顶进前,对线路常采用的加固方法有()。
ThefirstyearaftertheGreatRecession,2010,markedthehistoricalpeakofcollegeanduniversityenrollmentintheUnitedSt
以峻闻名,主峰峻极峰海拔1491.7米,古有“峻极于天”之说的是()。
团队过程的主要范畴是()。
下面5个历史事件发生在同一年的是()。(1)毛泽东抵重庆与蒋介石谈判(2)联合国成立(3)日本无条件投降(4)苏联第一颗原子弹爆炸成功(5)联合国教科文组织成立
设有定义:intx=0,*p;紧接着的赋值语句正确的是
最新回复
(
0
)