Phonon Engineering at The Nanoscale Makes Silicon a Better Thermoelectric Material

論文發表人：余人侃 (加州理工學院化學系博士班)

 

http://www.mrs.org/s_mrs/index.asp

 

矽一直以來是被認定為效率極低的熱電材料，其熱電係數僅有0.01。 然而，最近的研究發現，奈米矽線的熱電係數可提高至1.0。此熱電係數與商業上常用的碲化鉍熱電材料有著相近的效能。相對於傳統矽材料，奈米矽線的熱電效率高出兩個數量級，此效率上的提升主要來自於因為聲子與材料邊界碰撞頻率增加或聲子維度降低造成之導熱係數降低的影響。

本研究中，我們提出一個全新的奈米矽材料作為熱電材料: 矽奈米網。此結構是利用超磊晶奈米線模組轉移技術製成。其結構包含 34 奈米週期的二維孔洞陣列，每孔洞直徑約為14奈米。該材料實為一種聲子晶格材料。經測量發現，此結構室溫下的導熱係數為 1.7 W/m-K。此數值僅為相同等大小的矽奈米線導熱係數的一半。我們認為此現象係為聲子能階結構因週期孔洞而造成改變，使得聲子群速度降低的結果。因導熱係數的降低，此矽奈米網結構將有著較矽奈米線更高的熱電效率。這也是首次奈米聲子晶格結構在熱電材料上面的應用。

 

Bulk silicon has long been considered a poor thermoelectric (TE) material with the thermoelectric figure-of-merit as low as ZT=0.01. Nevertheless, it has been demonstrated recently that silicon nanowire boasts a ZT=1, comparable to commercially available Bi2Te3 TE devices. The enhancement mainly comes from the nearly two orders of magnitude reduction in thermal conductivity, possibly due to the dimensionality crossover of the phonon modes and/or the increased phonon-boundary scattering.

Here, we study the thermoelectric properties of a novel hole-bar-like silicon thin film (thickness ~ 25 nm). The hole-bar structure consists of a 2-D periodic array of 14 nm wide holes at a pitch of 34 nm, made by Superlattice Nanowire Pattern Transfer (SNAP) technique. This phononic-crystal material exhibits thermal conductivity as low as 2 W/m-K at 300K, which is 3.5 times smaller than that of nanowires with similar dimensions (k~7W/m-K, wire diameter = 22 nm). We attribute this reduction of thermal conductivity to the modification of phonon energy bands by the periodic hole-bar structure. This is the first such demonstration of the TE enhancement mediated by a nanoscale phonon crystal.

 

PRECISION NON-CONTACT DYNAMIC MEASUREMENT OF CASIMIR FORCE BETWEEN A METALLIC SPHERE AND SEMICONDUCOR PLATE

論文發表人：張家誠 (加州大學河濱分校物理所博士班)

 

http://meetings.aps.org/Meeting/MAR10/Event/123649

 

CASIMIR力量 是來自於量子真空下的產物,當尺寸趨向奈米或微米時CASIMIR力量就愈趨重要,為了要精準量測到CASIMIR力量,我們將使用高真空短同調光源干涉儀去精準測量, CASIMIR力量在金屬球與半導體之間的關係. 同時間,實驗數據與 Lifshitz 理論的比較也會在此討論. 此結果可以幫助我們找到在微機電系統中找到應用

 

A dynamic measurement of the Casimir force between a gold coated sphere and Si plate performed by using a high vacuum based short coherence light source interferometer will be presented. The comparison of results with Lifshitz theory will be discussed. The results will find application in  the design of MEMS (Micro Electro-Mechanical Systems).

Personal Pronoun Interchanges in Mandarin Chinese Conversation

論文發表人：蕭季樺 (加州大學洛杉磯分校/應用語言學所)

 

http://www.aaal.org/

 

自然口語中的語言使用往往與傳統語法的描述有所不同，人稱代名詞即是一例。在對話中，說話者常常使用第一人稱，我，以指涉聽話者;反之，使用第二人稱，你，指涉自己。本文探討第一及第二人稱代名詞互換的語用及語法功能。本文發現，人稱代名詞互換是為了達到高度的溝通: 說話者使用第一人稱指涉聽話者通常是轉述對方的內心話語，表現充分理解對方的立場;當說話者使用第二人稱指涉說話者，則是為了將聽話者帶進說話者自身的主觀經驗，使之更清楚地體現給聽話者。此語用功能與其句法環境相關。第一人稱指涉聽話者通常伴隨著感官-認知-語談動詞以及無指示性代名詞；反之，第二人稱指涉說話者本身的環境正好互補，通常有指示性代名詞，但是沒有感官-認知-語談動詞。語用與句法的相互影響在本文中也再次得到映證。

 

Traditional grammarians assert that conventional meanings of personal pronouns belong to linguistic codes, and their references depend on the context in which they are uttered. However, conversational uses of personal pronouns I and you often blur the traditional distinction between speakers and hearer(s). With discourse analysis and conversational analysis (Sacks, Schegloff and Jefferson 1974) as theoretical framework, this paper explores the recurrent switch of the first person singular pronoun wo, 'I', and the second person singular pronoun ni, 'you' in Chinese everyday conversation to illuminate how personal pronouns are employed to affect others' perspectives in order to enhance interaction in subsequent utterances. The following conversation excerpt nicely represents this phenomenon:

[Acting in a play]

Wang:  'He (Ming) would say, he— he — gives comments when I am acting, he will tell you how to make the playing even better.'

 

Speaker Wang is narrating his relation with another actor Ming in response to the radio show host's question of how their co-opetition relationship: Wang uses ni in reference to himself, as if the hearer, (i.e., the host), where him, and was receiving Ming's acting suggestions.

 

This paper examines the formal syntactic properties and discourse functions of the interchanges in the micro-organization within conversation and illuminates how personal pronouns are employed to affect others' perspectives in order to enhance interaction in subsequent utterances. The result shows that wo for the second person pronoun serves a communicative purpose by having speakers take listeners' perspective; on the other hand, ni for the first person pronoun is for information-providing purposes that invites listeners to a subjective experience. The syntactic characteristics within each interchange pattern correspond with one another, and together they explain the pragmatic functions of why speakers adopt the reverse perspectives contrary to the original meanings of wo and ni.

 

An efficiency analysis of a novel thermal energy harvesting device

論文發表人：許晉睿 (加州大學洛杉磯分校機械與航太工程系博士班)

 

http://spie.org/smart-structures-nde.xml

 

我們針對一種獨特的熱磁集能元件進行基礎研究及效能分析。此元件係利用軟磁材料之熱磁能耦合效應進行集能，過程中此材料於鄰近居禮溫度範圍內進行熱循環，進而使得材料之磁透率在相同頻率下進行循環，最終使得材料與一永久磁鐵間產生週期性的磁力吸引。我們設計釓(一種於室溫範圍下發生二階相變之材料)之單一磁區奈米結構尺寸，並將其製造成奈米結構陣列來提高元件之集能轉換效率，而奈米結構之特性則以超導量子干涉儀及磁力顯微鏡進行量測。此分析結果可用來建立解釋巨觀(有磁壁)結構與微觀(無磁壁)結構間能量差異之理論模型。

 

We report on fundamental study and efficiency analysis of a unique thermomagnetic energy harvesting device. This system relies on the coupling effect between magnetic and thermal energy within a soft ferromagnetic working body to harvest energy. While in operation, the working body of this device is thermally cycled about its Curie point, such that its magnetic susceptibility is also cycled at the same frequency. The resulting phenomenon is a periodic magnetic force of attraction between the working body and a permanent magnet. Based on the geometric design of single domain nanostructure, we fabricate the Gadolinium (Gd) working body, which undergoing a second order phase transformation for energy harvesting in the room temperature range, into a nanostructure array to increase the conversion efficiency. Characterization of the nanostructures is performed using both a SQUID and a Magnetic Force Microscope (MFM). These data can be used to develop analytical models to explain the energy differences between macroscopic structures (with domain walls) and nanoscale structures (without domain walls).

 

 

 

State Capacity and Primary Education: The Case of the Middle East and North African (MENA), 1960-2001

論文發表人：平思寧（克萊蒙大學政治與政策研究所博士班）

 

http://www.isanet.org/

 

教育的重要性已無庸置疑，但在現今多數的發展中國家仍未能達到全面基礎教育的基本目標。國家藉由有效的教育政策實施，而達成教育體系的完善，例如免費，義務教育以及國家對於教育預算最低門檻等。然而，鮮少研究探討：在這些法令政策的規定之外，初等教育最終的成果如何依賴國家政府的運作？本文旨在主張，國家僅制訂教育政策是不足以促進全面基礎教育的終極目的，特別在中東北非國家(Middle East and North Africa, MENA)中，我們見到了教育政策的頒佈與最後教育結果產出之矛盾，而本文則提出：「國家能力」限制了國家推行政策效率，進而阻礙學童參與教育的目的。有能力的國家，在政策制訂之外，更能以實際的執行能力，達到高入學率的初等教育目標。本文針對現今多數開發中仍未能達到全面普及化，但極其重要的初等教育為研究目標，以「國家能力」為解釋變數，探討在排除政策制訂後，能力較高的國家較能提昇國內初等教育的參與率。有鑑於中東北非國家特殊的經濟與文化背景，本文選擇該區為個案研究地區，期望能解釋該區在教育表現產出的特殊現象。

 

The importance of education cannot be emphasized more; however, to date many developing countries still do not achieve the basic goal of universal of primary education which is the most crucial and fundamental root of education. Implementation of education policies, such as free and compulsory education, or minimum education expenditure, regulates a country's education system. However, few studies ask what else a government can do after the inefficiency and inadequacy of relevant policies. In this study, through the case study of the Middle East and North African (MENA) region, we argue that given that a government's commitment to education is important, countries with higher state capacity performance in promoting and reaching higher primary education enrollment rate.

Analyzing China's Participation in the World Trade Organization: A Constructivist Approach

張文揚、Claremont Graduate University、Department of Politics and Policy

 

http://www.spsa.net/

 

經濟整合與貿易自由化是兩個需要持續交涉與合作的領域，因為主權國家必須調整他們的國內外政策以配合他們的經濟貿易伙伴。爰此，中國大陸在兩千零一年加入世界貿易組織成為本文的研究對象，以分析中國如何以漸進的學習過程進入到全球經濟與現有的貿易規範之中。本文將檢視江憶恩(Alastair Iain Johnston)針對中國參與國際制度的理論。藉由應用三個重要的個體過程：模仿、社會影響、與勸說，本文旨在探討中國近年加入世界貿易組織的社會化過程。我們將世界貿易組織視為一個社會化過程發生的制度環境。在本文中，世界貿易組織的法律架構與與官方文件被視為是行為者互動的結構。最後，社會化過程發生在中國與其他行為者、以及現有規範的互動之中。模仿、社會影響與勸說是三個重要的面向，在本文中也將分別檢驗。結論則提出中國參與世界貿易組織的政策意涵與對這三個過程的評估。

 

Economic integration and trade liberalization are two issue areas that require constant negotiations and cooperation, for which nation states have to adjust their domestic and foreign policies according to their partners. China's entry into the World Trade Organization (WTO) in 2001 can therefore serve as a good example, which shows the gradual learning process of China to embed in global economy and the existing trading regulations. This paper will test Johnston (2008)'s theory on China in international institutions. By applying three important micro processes--mimicking, social influence, and persuasion--the research paper aims at exploring the socialization process of China in the WTO during the recent years. We treat the WTO as an institutional environment where this socialization process occurs. In this study, the legal framework and official documents of the WTO are considered as the structure that interacts with agents in this study. Finally, the socialization processes take place during China's interaction with other actors and with the existing norms. Mimicking, social influence, and persuasion are three important aspects, which will be separately dealt with in later part of this paper. The evaluation of these processes and policy implications about China's participation in WTO will be provided at the end.