託福閱讀背景材料彙總

大家在備考託福的閱讀時會去積累一些背景資料，好幫助我們對此類題型有一定的瞭解，下面小編給大家帶來託福閱讀背景材料彙總，希望喜歡。

託福閱讀背景材料:距離土星第七遠的土星衛星

Excitement Builds for the Possibility of Life on Enceladus

Scientists tackle the question of how to search for life on Saturn’s sixth-largest moon

By Annie Sneed on June 28, 2016

Saturn's icy moon Enceladus is thought to host a liquid ocean beneath its frozen surface that could be hospitable to life. Credit: NASA

Saturn’s frozen moon Enceladus is a tantalizing world—many scientists are increasingly convinced it may be the best place in our solar system to search for life. NASA’s Cassini spacecraft, currently orbiting Saturn, has made intriguing observations of icy jets spewing from a suspected underground liquid ocean on the mysterious world that might be hospitable to alien life.

Cassini’s tour is due to wind down in 2017, and scientists badly want to send a dedicated mission to Enceladus to look for signs of life. In fact, some have already started seriously thinking about exactly how they might do this—including planetary scientist Carolyn Porco, who is the imaging team leader for Cassini. Earlier this month, she gathered a group of researchers including oceanographers, organic chemists and astrobiologists at the University of California, Berkeley, to strategize how to search for extraterrestrials on Enceladus—which, according to Porco, “is a total bitch of a problem to solve.”

Although Enceladus is small in size and shrouded in a thick shell of ice, it appears to be a habitable world: It has a source of energy from friction created by its orbit around Saturn, organic compounds that are building blocks for life and a liquid water ocean underneath all that ice. But just because Enceladus may be hospitable to life does not mean life exists there; it will take much more work to definitively prove it. At the Berkeley meeting, scientists laid out the data Cassini has collected for Enceladus—they discussed analyses of its geysers, measurements of its ice shell, ideas on what its ocean chemistry might be like, and more. Yet even with all the newest data and models scientists have, they are not even close to detecting organisms on Enceladus—hence the need for a space mission.

Finding life there would be a profound revelation that we are not alone in the cosmos. Furthermore, the discovery of organisms—or the lack thereof—could answer the subtler mystery of how life started on Earth. Researchers at the meeting presented two major opposing theories about how life here originated (in the ocean versus on land), and the group discussed how exploring Enceladus would inform this debate. “It would be a test of one of the ideas about the origin of life,” Porco says—specifically, the proposition that Earth’s species sprang in the sea. For example, if organisms exist in Enceladus’s ocean and presumably arose there, it would support the theory that life began on Earth in hydrothermal vents (hot, nutrient-rich, deep-sea vents on the ocean floor) rather than in patches of water on land.

　　託福閱讀背景材料：甲烷水合物

Gas Hydrate

Gas Hydrate又稱甲烷水合物(Methane Hydrate)系水分子與甲烷於低溫高壓(0℃，26大氣壓或10℃，76大氣壓下)形成類似冰狀物質，在常溫常壓下即分解成水與甲烷，Gas Hydrate在水深數百公尺的大陸邊緣地區存在如太平洋海域之大陸邊緣，大西洋的大陸斜坡，南極大陸周邊海域，Kvenvoden 1996年估計Gas Hydrate總儲量爲1 x 1016(m)3，如能夠開採將成爲重要之能源，因爲甲烷爲溫室效應氣體，故其與全球氣候之變化將爲海突候之變化將爲海洋鑽探研究之重點。Gas Hydrate之存在與海底之穩定性亦有密切之關係。

什麼是甲烷水合物

「可燃燒的冰塊」，這是許多人在介紹甲烷水合物時很喜歡引用的標題。在實驗中人工合成的甲烷水合物就像一塊不透明的冰塊般純白、潔淨，在室溫下一點火，它就自我燃燒起來(圖一)。嚴格說來，甲烷水合物指的是甲烷氣體分子在高壓及低溫的狀態下，被呈籠狀晶結架構的水分子所包合，而形成一種類似冰晶的化合物。這種氣體分子和水分子的結合並不依靠化學的鍵結，純粹是氣體分子被包裹在水分子的籠狀架構空隙中，與一般化學反應所產生的水合物性質並不相同。有的學者因而認爲應稱其爲「甲烷氣水包合物」(methane clathrate)，以別於一般以化學鍵方式結合的水合物。另外，大自然中與水分子結成籠狀包合物的氣體分子並不限於甲烷，乙烷、丙烷等烷氫類氣體，甚至二氧化碳、氮氣等常見氣體，在適當的高壓低溫條件下，均會與水分子結合成氣水包合物。事實上，這類氣水包合物的英文名稱爲「gas hydrate」，直譯應爲「天然氣水合物」或「瓦斯水合物」。由於自然界中的天然氣水合物其氣體成份以甲烷爲主(超過90%)，因此一般人常把氣水包合物稱爲「甲烷水合物」。本文隨俗，用「甲烷水合物」代表學理上較嚴謹的「天然氣氣水包合物」一詞。

　　託福閱讀背景材料：納米材料及其應用

About 納米材料及其應用

納米技術在生物工程上的應用

衆所周知，分子是保持物質化學性質不變的最小單位。生物分子是很好的信息處理材料，每一個生物大分子本身就是一個微型處理器，分子在運動過程中以可預測方式進行狀態變化，其原理類似於計算機的邏輯開關，利用該特性並結合納米技術，可以此來設計量子計算機。美國南加州大學的Adelman博士等應用基於DNA分子計算技術的生物實驗方法，有效地解決了目前計算機無法解決的問題—“哈密頓路徑問題”，使人們對生物材料的信息處理功能和生物分子的計算技術有了進一步的認識。

雖然分子計算機目前只是處於理想階段，但科學家已經考慮應用幾種生物分子製造計算機的組件，其中細菌視紫紅質最具前景。該生物材料具有特異的熱、光、化學物理特性和很好的穩定性，並且，其奇特的光學循環特性可用於儲存信息，從而起到代替當今計算機信息處理和信息存儲的作用。在整個光循環過程中，細菌視紫紅質經歷幾種不同的中間體過程，伴隨相應的物質結構變化。Birge等研究了細菌視紫紅質分子潛在的並行處理機制和用作三維存儲器的潛能。通過調諧激光束，將信息並行地寫入細菌視紫紅質立方體，並從立方體中讀取信息，並且細菌視紫紅質的三維存儲器可提供比二維光學存儲器大得多的存儲空間。

到目前爲止，還沒有出現商品化的分子計算機組件。科學家們認爲：要想提高集成度，製造微型計算機，關鍵在於尋找具有開關功能的微型器件。美國錫拉丘茲大學已經利用細菌視紫紅質蛋白質製作出了光導“與”門，利用發光門製成蛋白質存儲器。此外，他們還利用細菌視紫紅質蛋白質研製模擬人腦聯想能力的中心網絡和聯想式存儲裝置。

納米計算機的問世，將會使當今的信息時代發生質的飛躍。它將突破傳統極限，使單位體積物質的儲存和信息處理的能力提高上百萬倍，從而實現電子學上的又一次革命。

有關納米技術

華人科學家：美國納米技術應用研究四大熱點

正在美國從事納米技術研究的華人青年科學家崔屹博士17日接受新華社記者採訪時表示，美國納米技術的應用研究目前正在半導體芯片、癌症診斷、光學新材料和生物分子追蹤等四大熱點領域快速發展，其中在芯片和癌症診斷領域的應用可望在10年內出現劃時代的突破。

崔屹說，在癌症研究領域，利用納米技術製成的傳感器可望使各種癌症的早期診斷成爲現實。目前，崔屹和他的同事已經在實驗室環境下實現了對前列腺癌、直腸癌等多種癌症的早期診斷。納米傳感器靈敏度很高，在進行血液檢測時，當傳感器中預置的某種癌細胞抗體遇到相應的抗原時，傳感器中的電流會發生變化，通過這種電流變化可以判斷血液中癌細胞的種類和濃度。這一研究成果可望於近期發表在美國《科學》雜誌上。崔屹指出，目前越來越多的風險投資正在涌入這一領域，但這一技術在實用中還有一些技術難題需要解決。他估計，今後可能會有多種納米傳感器集成在一起被置入人體，以用來早期檢測各種疾病。

在半導體芯片領域，如何讓芯片體積更小、速度更快是科學界一直研究的課題。目前用於芯片製造的光刻技術已經接近於發展極限，要想把更多的晶體管集成到一塊芯片上已經越來越難。目前，美國納米技術專家們試圖把納米級的半導體材料做成晶體管，從而可以讓一塊芯片上容納更多的晶體管。這種芯片的運算速度可望比傳統的硅芯片提高上千倍。這一研究方向在2001年取得基礎性研究突破後，目前在應用研究中越來越熱。據崔屹估計，這一技術可望在10年後達到實用化。

此外，納米技術在光學材料和生物分子追蹤兩個領域的應用也是研究熱門。在光學材料研究領域，科學家們試圖改變某些半導體材料的分子結構，用來生產特定的光學器件。比如，一些科學家試圖讓某種半導體材料內部具有納米級的線狀結構，這種材料用於顯示器製造領域可以大大提高顯示器的清晰度和顏色逼真度。而在生物分子追蹤領域，科學家把某種納米顆粒“粘”在生物分子上，然後利用納米顆粒的發光特性研究生物分子的行蹤。這對研究艾滋病病毒等在人體內的活動過程十分有益。

崔屹說，美國在納米應用研究領域中享有資金和人才優勢，一直走在世界前列，但距離納米技術實用化仍有一段路要走。與美國相比，其他國家則主要處於納米技術的基礎研究階段。

現年27歲的崔屹畢業於中國科技大學，後在哈佛大學獲納米應用專業博士，目前在加州大學伯克利分校從事研究工作。過去幾年，崔屹在《自然》和《科學》等權威雜誌上發表多篇研究論文，同時還是2003年美國“米勒”傑出青年科學家獎和2001年美國材料研究學會金獎得主。

　　託福閱讀背景材料：p53的抗癌作用

What is p53 ?

After the identification of the p53 protein and the subsequent cloning of p53 genes from several species, early observations suggested that p53 may function as an oncogene, because overexpression of p53 appeared to cause oncogenic transformation of cells. In the late 1980s, however, several critical discoveries defined the normal function of p53 to be anti-oncogenic. Wild-type p53 genes, when introduced into cells, were found to be growth suppressive. The screening of DNA from colon cancer patients revealed that p53 mutations occur with unusually high frequency in tumor tissue, an observation that was extended to most of the other major forms of human cancer. Indeed, members of Li-Fraumeni cancer-prone families were shown to carry germ-line p53 mutations. The importance of these observations was underscored by the finding that mice that are homozygous null for p53, although developmentally competent, are highly predisposed to tumors.

The functional character of the p53 protein was determined by experiments showing that p53 contains a strong transcriptional activation domain within its amino terminus and that it is a tetrameric, sequence-specific DNA-biding protein with a defined cognate binding site containing two copies of the 10-mer (5'-RRRCA/TT/AGYYY-3'). Although the p53 protein acts as a transcriptional activator of genes containing p53-binding sites, it is also capable of strongly inhibiting transcription from many genes lacking p53-binding sites. Several oncogenic DNA viruses express viral gene products that associate with and inhibit the trans-activation function of p53, notably SV40 large T antigen, the adenovirus E1B 55-kD protein, and the E6 protein of oncogenic forms of human papillomavirus (HPV E6). In cells, p53 can associate with a 90-kD protein, identified as the product of the mdm-2 oncogene, which is amplified in some types of tumors. When bound to mdm-2, p53 can no longer function as an activator of transcription.

p53 plays multiple roles in cells. Expression of high levels of wild-type (but not mutant) p53 has two outcomes: cell cycle arrest or apoptosis. The observation that DNA-damaging agents induce levels of p53 in cells led to the definition of p53 as a checkpoint factor, akin, perhaps, to the product of the fad9 gene in yeast. While dispensable for viability, in response to genotoxic stress, p53 acts as an "emergency brake" inducing either arrest or apoptosis, protecting the genome from accumulating excess mutations. Consistent with this notion, cells lacking p53 were shown to be genetically unstable and thus more prone to tumors.