搜题请搜索小程序“爱下问搜题”
问题 问答题 简答题

判断并机UPS环流大小的标准是什么？

答案

参考答案：

（l）各台UPS所输出电流的总和与从UPS的并机输出总线上的输出电流的差值；

（2）各台U-PS单机的输出功率因数应该是稳态值，而不应是可变值。

单项选择题

假设市场中有两种债券A和B，债券A的票面收益为8%，债券B的票面收益为10%，两种债券的其他要素均相同，那么，下列说法中正确的是（）。

A.债券A和债券B的久期相等

B.债券A的久期比债券B的久期短

C.债券A和债券B的久期不可比

D.债券A的久期比债券B的久期长
查看答案
问答题

The Web Way to Learn a Language


The young woman seated next to us at a bar revealed a vaguely exotic(异国的) air; her looks and style, we thought, made it likely that she was not American born. But then she spoke in perfect American English, even ending her declarative sentences in that rising questioning tone of many young Californians. As it turns out, however, she wasn’t from these parts after all; she was born in Iran and spoke only Farsi(波斯语) until her arrival here two years ago. What classes, we wondered, had she attended to learn the language so well
"I didn’t," she said. "I used RosettaStone." Those yellow boxes sold at shopping-mall may be the most recognizable example of PC-based language learning, but it certainly isn’t the only one. With the growth of Internet connectivity and social networks, companies have introduced a wide range of Internet-based language learning products, both free and fee-based, that allow students to interact in real time with instructors in other countries, gain access to their lesson plans wherever they are in the world, and communicate with like-minded virtual pen pals who are also trying to remember if bambino means baby.
Learning a language sometimes seems as difficult as dieting. The solution is to figure out how to stay interested after the novelty wears off. To counter boredom, online language programs have introduced crossword puzzles, interactive videos and other games to reward users for making progress.
Online courses are either fee-based, free or a combination. Starter packages of fee-based programs may cost just a few hundred dollars, but the cost to reach higher levels of comprehension and speaking can easily be $1,000. While that may sound expensive, language company executives say it isn’t; college courses often cost many thousands of dollars to reach the same level. So, cost aside, how do you choose which program to use The answer is that one size doesn’t fit all.
"The quality of feedback is important," according to Mike Levy, head of the school of languages and linguistics at Griffith University. "Sites with human contact work best," he said. "This shows the advantage of humans compared to computers. A computer is never as subtle or intelligent."

Pay and learn


RosettaStone, the best-known language program, now offers a $1,000 product that includes RosettaCourse, a traditional lesson-based module; RosettaStudio, a place where a user can talk to a native speaker via video chat; and RosettaWorld, an online community where you can play language-related games.
"We offer modern-day pen pals facilitated with voice," said Tom Adams, the company’s chief executive.
RosettaStone uses things like colorful flash cards to help students first learn basic words, and then connect those words to concepts and sentences. The idea, according to Mr. Adams, is for the user to let go of the adult "technical questions and just get into a comfort zone, learning new sounds and trying to make sense of them."
One of RosettaStone’s main competitors, TellMeMore, believes it has an advantage because its software not only teaches words and phrases, but includes a speech recognition component that analyzes pronunciation, presents a graph of speech, and suggests how to perfect it. Other videos show students how to shape their mouths to create sounds difficult for native English speakers, like the rolling R in Spanish. With 10 levels of content, a 10,000-word vocabulary, videos of native speakers and more than 40 practice activities, TellMeMore believes it has enough material to keep a user motivated.
TellMeMore charges $390 for a year’s access to its resources for six languages; those looking for a quick refresher can buy a $10 daily pass. Weekly, monthly and half-year passes are also available.
The company’s product is currently available only on CD-ROM, but online versions for both Mac and Windows that will include real-time coaching are coming later this year.

Free now, pay later


Livemocha, a two-year-old Web start-up, offers free basic lessons in 30 languages. Users can apply for advanced courses with additional features on a monthly or six-month basis. For $20 a month, students can submit up to eight voice recordings to a native-speaking tutor, who will then review and make recommendations for improvement within 24 hours. For $70 every six months, students can submit up to two examples a lesson.
All students, whether using the pay or free model, can join social networking groups and speak live to people around the world who are native speakers interested in learning English. As with all social networking sites, this feature is open to misuse. Within hours of signing up for Livemocha, I received a note from a young woman, ostensibly (假装的) from Poland, "wanting to meet me."
The company says it has "the world’s largest community of people learning languages," with five million registered users in 200 countries.
Financed in part by the European Union, Babbel offers paid instruction (and a free trial lesson) in English, French, German, Italian, and Spanish for $12 a month, or $6.62 a month for a six-month commitment. In addition to extended grammar and vocabulary, users can communicate with others in their desired language via private or public chats, or arrange to get in touch via voice.

Free language learning


If money is truly an object, a variety of free language learning is available from a number of sites. The British Broadcasting Corporation offers varying levels of instruction for 36 languages, with features including audio and video playback and translation. Looking to visit Deutschland The German television network, Deutsche Welle, can help you make yourself understood. And for those who not only want to learn another language but another alphabet as well, try japanese-online.corn, or learn-korean.net.

Applications for a smartphone


No program would be complete without an accompanying smartphone application, and many exist for the iPhone and other devices. Several are simple providers of useful phrases, including the Lonely Planet Phrasebooks, the Oxford Translator Travel Pro, and World Nomads. The Ultralingua Translation Dictionary offers simultaneous translation of English and six languages. Both RosettaStone and TellMeMore say that they are developing smartphone applications as supplements to their online programs, but neither has announced a release date.
Livemocha expects to have an application later this year for both the Android and iPhone operating systems. The company plans on integrating text with a native speaker pronouncing the language, and providing the option for voice recording and live video feeds.

Neither RosettaStone nor TellMeMore has announced when to______smartphone applications.
查看答案