Portfolio 3
Recently, I have read an article about solar energy, which mainly tell me the importance of solar energy and the current efficiency of using solar energy. Here is a summary of the article.
As we all know ,the sun is the most powerful source of energy. Even though only small fraction of the sun' s power reaches the earth, it produces "10,000 times as much as all the commercial energy that humans use on the planet", the article says.
The importance of the solar energy is because it is sustainable and clean. Those fossil fuels cannot remain the dominant sources of energy forever. Whatever the precise timetable for their depletion, oil and gas supplies will not keep up with growing energy demands. Coal is available in abundance, but its use exacerbates air and water pollution problems, and coal contributes even more substantially than the other fossil fuels to the buildup of carbon dioxide in the atmosphere.
For a long-term, sustainable energy source, solar power offers an attractive alternative. Its availability far exceeds any conceivable future energy demands. It is environmentally clean, and its energy is transmitted from the sun to the Earth free of charge. But exploiting the sun’s power is not without challenges. Overcoming the barriers to widespread solar power generation will require engineering innovations in several arenas — for capturing the sun’s energy, converting it to useful forms, and storing it for use when the sun itself is obscured.
The article take solar cell as an example to describe the current situation of solar energy usage. Solar photovoltaic cell is one of the popular production nowadays, which direct produce electric current from captured sunlight. However, today's commercial solar cells typically convert sunlight into electricity with "an efficiency of only 10 percent to 20 percent"[Schaller et al]. Given their manufacturing costs, modules of today’s cells incorporated in the power grid would produce electricity at a cost roughly "3 to 6 times higher than current prices, or 18-30 cents per kilowatt hour" [Solar Energy Technologies Program]. To make solar economically competitive, engineers must find ways to improve the efficiency of the cells and to lower their manufacturing costs.
The author points out the bright future of solar energy at the last line, solar energy provides less than 1% of the world's total energy, but it has the potential to provide much much more.
References
Make solar energy economical. Retrieved October 1st, 2008, from http://engineeringchallenges.org/cms/8996/9082.asp
DOE. Solar Energy Technologies Program Multi-Year Program Plan 2007-2011. Office of Energy Efficiency and Renewable Energy. Washington, D.C.: DOE.
Schaller, R.D., and V.I. Klimov. 2004. High Efficiency Carrier Multiplication in PbSe Nanocrystals: Implications for Solar Energy Conversion. Physical Review Letters 92(18): 186601-1 - 186601-4. DOI: 10.1103/PhysRevLett.92.186601
Monday, September 29, 2008
Monday, September 8, 2008
portfolio 2 grammar exercise--article
This is _an__ easy question.
Please speak __a_ little louder.
May I have your __n/a_ phone number?
I have never seen _a_ UFO.Answera
May I ask you __the_ question?Answera
David is _the__ best student in our class.
What is _the__ name of the next station?
He has __n/a_ my car today.
I went to __the_ sea during my summer vacation.
Is there _a__ public telephone near here?
This is _an__ easy question.
Please speak __a_ little louder.
May I have your __n/a_ phone number?
I have never seen _a_ UFO.Answera
May I ask you __the_ question?Answera
David is _the__ best student in our class.
What is _the__ name of the next station?
He has __n/a_ my car today.
I went to __the_ sea during my summer vacation.
Is there _a__ public telephone near here?
Portfolio 2 Grammar Mistake--ARTICLE
The most common mistakes I always made is the usage of the article. I am not sure which article should be used with noun sometimes. Now I would like to explain the grammar in order to avoid the misusing in the future.
In general, there are two kinds of articles: definite and indefinite. The definite article "the" can be singular or plural. The indefinite article "a" or "an" is singular, and cannot be used with a plural noun.
"A" or "an" is used with a singular count noun when you mean "one of many," "any," ,such as, a bus, an apple.Also, use "a" or "an" the first time you use a noun in a paragraph
"The"is used with any noun when the meaning is specific,when the noun names the only one of a kind, for example, the earth.In addition,Use "the" the second time you use that same noun in the same paragraph.
When I struggle with articles in my writing, I always remind me of the most basic rule.That is , "the" should be used for specific nouns, when your reader knows exactly which one you are referring to, or for nouns of which there is only one. "A" or "an should be used for general nouns, or when your reader does not know exactly which one you are referring to. Here is some examples to illustrate the basic rule.
"A bear is a mammal". In the above sentence, we do not know which pig the writer is referring to. Therefore, the writer should use "a", instead of "the".
"The bear is running in the street". In this situation, we know which bear the writer is referring to(the bear running in the street), which means that the writer can use "the", instead of "a".
"The teddy bear is a toy bear". In a situation like this, there is only one teddy bear in the world, so the writer can use "the" instead of "a", and we will still know exactly which "bear "he is talking about .
I hope i have explained the grammar clearly and there is no article mistakes in this writing!
The most common mistakes I always made is the usage of the article. I am not sure which article should be used with noun sometimes. Now I would like to explain the grammar in order to avoid the misusing in the future.
In general, there are two kinds of articles: definite and indefinite. The definite article "the" can be singular or plural. The indefinite article "a" or "an" is singular, and cannot be used with a plural noun.
"A" or "an" is used with a singular count noun when you mean "one of many," "any," ,such as, a bus, an apple.Also, use "a" or "an" the first time you use a noun in a paragraph
"The"is used with any noun when the meaning is specific,when the noun names the only one of a kind, for example, the earth.In addition,Use "the" the second time you use that same noun in the same paragraph.
When I struggle with articles in my writing, I always remind me of the most basic rule.That is , "the" should be used for specific nouns, when your reader knows exactly which one you are referring to, or for nouns of which there is only one. "A" or "an should be used for general nouns, or when your reader does not know exactly which one you are referring to. Here is some examples to illustrate the basic rule.
"A bear is a mammal". In the above sentence, we do not know which pig the writer is referring to. Therefore, the writer should use "a", instead of "the".
"The bear is running in the street". In this situation, we know which bear the writer is referring to(the bear running in the street), which means that the writer can use "the", instead of "a".
"The teddy bear is a toy bear". In a situation like this, there is only one teddy bear in the world, so the writer can use "the" instead of "a", and we will still know exactly which "bear "he is talking about .
I hope i have explained the grammar clearly and there is no article mistakes in this writing!
Tuesday, September 2, 2008
Portfolio_task1
I have read two articles describing the future of engineering. The former one introduced the grand challenges for engineering, while the latter one explained how the world is expanding for engineers. I prefer the latter one, which told us the world is offering more chances to our engineers.
Engineers are trained to systematically analyse complex sets of information and to apply systems and critical thinking in designing solutions. With these kind of positive attributes, engineers are able to meet the need of various careers. As the world economy diversifies, careers choices for engineers are also widen. Engineers are around every corner of our society. from manufacturing sectors to associated sectors, then to service sectors, we can see the scope of engineers has been broadened. The reason why engineers are so widely employed is engineers represent a kind of workforce that do not afraid of new technology but embrace and thrive on it. It is just the quality which most factories, companies, organisations and even nations require.
Challenge are always together with chances. 14 grand challenges such as global warming, the increasing need of clean water, energy, food, information security, are introduced in the first article. All the challenges above are global and extremely important. However, they are jobs left for engineers to solve. The great challenges await for engineers reflects indirectly the importance of engineers. As our society improves, engineers are going to play a more important role in the world.
I have read two articles describing the future of engineering. The former one introduced the grand challenges for engineering, while the latter one explained how the world is expanding for engineers. I prefer the latter one, which told us the world is offering more chances to our engineers.
Engineers are trained to systematically analyse complex sets of information and to apply systems and critical thinking in designing solutions. With these kind of positive attributes, engineers are able to meet the need of various careers. As the world economy diversifies, careers choices for engineers are also widen. Engineers are around every corner of our society. from manufacturing sectors to associated sectors, then to service sectors, we can see the scope of engineers has been broadened. The reason why engineers are so widely employed is engineers represent a kind of workforce that do not afraid of new technology but embrace and thrive on it. It is just the quality which most factories, companies, organisations and even nations require.
Challenge are always together with chances. 14 grand challenges such as global warming, the increasing need of clean water, energy, food, information security, are introduced in the first article. All the challenges above are global and extremely important. However, they are jobs left for engineers to solve. The great challenges await for engineers reflects indirectly the importance of engineers. As our society improves, engineers are going to play a more important role in the world.
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