全國中小學科展

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物理與天文學

二種液滴之凝固現象探討

有研究討論過氯化銨溶液液滴在低溫接觸面,液滴凝固後的頂部出現了圓頂、尖頂、在尖頂部分生出如煙囪般的結構,並提出模型加以討論,但實驗中的部分觀察結果卻和文獻提出的結果有所不同。 本作品使用25nm之二氧化鈦粉末製成之奈米流體液滴置於疏水性冷面,在低濃度(0.5 mg/mL)時,頂端形成尖頂;但在濃度超過1 mg/mL,凝固時由於馬拉哥尼流動,造成頂部形呈圓形平台,且此平台半徑隨著濃度上升而增加,另外在平台外緣堆積數量可觀的白色顆粒。 實驗中針對氯化銨溶液液滴及二氧化鈦奈米流體液滴在凝固時的顏色分布、動態接觸角變化,及頂端各種特殊外形加以分析,並用Hele-Shaw cell裝置觀察2種液滴的二維凝固過程,分析2種液滴凝固現象之變化原因及頂部特殊形狀的形成機制。

週期性變化磁場對複合磁體磁浮特性的影響

此研究期望找到穩定磁浮的方法及探討產生磁浮振盪的變因。首先利用吸附上鐵材的磁浮體,觀察其造成的磁浮減震。實驗過程藉由變動磁場,發現週期性變動的磁通量對鐵磁體的磁化及渦電流產生影響,進而改變磁振盪振幅及阻尼係數。研究結果得知磁場的交變頻率越大,會導致磁浮體所受斥力增加且鐵磁體形成的減振效果減緩。另外,複合磁體中受硬磁磁化的鐵磁體在頻率到達一定區間時才能觀察到渦電流的影響,而此區間受複合磁體排列、磁化強度等變因控制。

黏滯流體與固態粒子對馬克士威爾滾輪的物理影響及探討

將黏滯流體放入空心帶軸圓盤中(稱作黏流滾擺),以繩繞軸芯捲至25.17 cm高度落下,實驗發現填充量為22.500 %~87.500 %時,相對其他填充量以非常緩慢的速度落下且不會彈跳,而圓盤角速度具有週期性,並整合參考文獻理論公式分析邊界層對圓盤運動的趨勢,發現若邊界層變薄則讓液體質心處於α>0,滾擺加速滾動,若變厚,則反之。當釋放高度大於8.55cm無彈跳填充範圍將維持在22.500 %~87.500 %,不受高度影響。而黏流滾擺落下的時間約為空圓盤的122倍。改以黏滯性較小的水作為填充液體則不存在無彈跳填充區域。若改以填充混和質量濃度比例100:6及100:20的黏滯流體與水,則可發現臨界線向左偏移。若填充液體改為固態粒子(細沙),實驗發現填充比例為4.242 %~93.196 %時,細沙滾擺會固定於高空中而不落下。比較黏滯流體、水、細沙三種填充物質,黏滯流體緩衝效果與穩定性最佳。

陽光下的旋轉舞者——探討雙小行星的形成原因與其分佈之關聯

現研究認為雙小行星的形成原因為小行星受YORP效應(Yarkovsky–O'Keefe–Radzievskii–Paddack effect) 使自轉加速至裂解自轉週期後形成。此研究回推母小行星裂解自轉週期,推論雙小行星是否由YORP效應形成。結果呈現實際裂解自轉週期集中於1.4 – 2.4小時,較理想裂解自轉週期短。軌道半長軸0.5 – 3.5 AU,由YORP效應形成的雙小行星約佔總體73%,2.8 AU後無YORP效應產生的雙小行星。計算YORP效應產生的雙小行星佔總體比例分佈,呈現以1.8 AU為轉折點,轉折點前YORP比例接近,轉折點後比例隨與日距離增加持續下降。透過模擬YORP比例在長時間中的演化,呈現約107 年後YORP比例分佈出現轉折點,演化時間越久轉折點與日距離增加,透過轉折點可推論小行星受演化的時長,但現行模型仍無法考量雙小行星形成過程與演化造成的多重因素,此些效應會使演化時間加長。非YORP效應產生的雙小行星在科克伍德空隙前方增加,推測受木星軌道共振使碰撞機率增加產生雙小行星。

Can Quantum Mechanical Two-State Theory model Coulomb’s Force?

The quantum mechanical description of the four fundamental forces of nature is very important for the decryption of the rules which underlie our world. While Quantum Electrodynamics (QED) describes the electromagnetic force in great detail, it also uses complex mathematical techniques and advanced physical concepts. In the following, I will analyze to what extent a quantum mechanical two-state model can be used to describe the Coulomb interaction between two charged particles. To do so, I will exclusively focus on the electrostatic interaction, leaving dynamics aside. Furthermore, the analysis is nonrelativistic and does not consider the spin of the particles. Finally, using discrete state theory allows to explore the strength of the basic concepts of early quantum mechanics. In this sense, I will try to develop a simpli ed model for the quantum mechanical description of the electrostatic force. However, the analysis is not simplistic, since the traditional formalism of quantum mechanics will be used, including Dirac's Bra-ket notation, probability amplitudes, the Hamiltonian matrix as well as the Schrödinger equation. To understand the framework of my project, it may be helpful to take a look at the source of inspiration for my analysis: In Chapter 10 of the third volume of the well-known textbook series The Feynman Lectures on Physics[4], the force holding the hydrogen molecular ion together is explained in terms of a two-state system. The electron of the molecular ion can be either at the rst proton or at the second one. The exchange of the electron between both protons leads to an attractive force between them. It is known from QED that the electrostatic interaction between two charged particles is due to the exchange of a virtual photon which acts as force carrier. The idea of my work is to explore whether the electrostatic force can be described by a very similar model, replacing the electron acting as force carrier in the molecular ion by a virtual photon for the description of the electrostatic force between two charged particles. To describe a system consisting of charged particles, I will make the assumption that a charged particle can appear in two states. Either it is in state e where it can emit a photon or it is in state a which enables it to absorb a photon. Upon emission or absorption of a photon the charged particle transitions to the respective other state. This makes the approach analyzed in my work an element of discrete state theory, since two di erent states of the particle are used to store information about it. Of course such a model cannot be compared to the sophisticated theory of Quantum Electrodynamics. The point is, however, that it is interesting to explore the power of the most fundamental concepts of quantum mechanics and to show that such an analysis can lead to inspiring results.

製備自組裝單分子層修飾電極檢測水中銅離子之研究

本研究開發一種檢測水質之創新技術,利用電化學阻抗分析法檢測水樣中微量的銅離子。本實驗研究確知:當溫度越高,溶液的電阻值越小;離子濃度愈低,測得的溶液電阻值越大,且皆具有檢量關係,濃度量測極限可至10-6 M。此外,以鏈狀硫醇連結組胺酸之改質電極對銅離子皆相對具較佳辨識能力,又以 11-MUA改質電極靈敏度與量測極限皆最佳,最低濃度可量測至數量級10-8 M (約0.0019 ppm),遠低於現行銅離子流放標準。以效能最佳之11-MUA改質電極以環境水樣外加法量測不同銅離子濃度下之Rct值,發現兩者亦具有線性檢量關係,因此此檢測模組適用於環境水樣之檢測。 目前已確認此檢測模組適用於環境水樣中銅離子濃度之定量,未來期望拓展此檢測法於不同重金屬離子,以對不同離子具選擇性之單分子層材料修飾於電極表面,使此檢測模組能廣泛應用於水樣中常見重金屬離子之濃度檢測。

Analysis on a New Electric Field Measurement Method Using Ionic Propulsion Propeller

Given the high sensitivity of electronic instruments, electromagnetic field intensity measuring is now becoming an essential part of the industry. Current electric field intensity meters are unfit for individual use and focus mainly on electromagnetic radiation rather than the field itself. In ionic propulsion, the propulsion force is proportional to electric field intensity but the use of this property on measurement remains largely unexplored. Here, our team investigates ionic propulsion in electric fields generated by electro-static methods and then systematically varies the point of measurement inside the field, thereby altering the intensity of the field without focusing on electromagnetic radiation. By combining the Van de graaff generator with an adjustable ionic thrust propeller, we find that the propeller speed which is proportional to the electric field is directly determined by the electric field intensity. Furthermore, we applied stroboscopy to the system to measure RPM, and have achieved the direct interaction between field intensity and RPM, which could be a new meter for field intensity measurement.

外加電場下環形泡膜形變控制之研究

本研究利用平行電板建立電場,觀察在外加電場下環形泡膜的各種形變運動。電場越大時,形變越大;分別使用不同大小的環形框架觀察,發現形變量與框架半徑的比值會隨著框架半徑增加而減小,推論與表面電荷密度的分布變化有關連。將泡膜從薄到厚分成五個區域,針對不同厚度的泡膜與運動型態做分析,發現運動狀態可以大致分成,穩定震動、提升點,以及急遽增加後碰到電板破裂三個階段。針對電場26,666 V/m-33,333 V/m時的震動現象做深入分析,利用簡諧運動的模型來詮釋泡膜運動,藉以預測不同表面張力液體對應的彈性係數。未來期望利用不同電解質去改變泡膜組成,探討不同電解質在電場下的運動行為。

液滴懸浮於移動表面現象之探討

液體無固定形狀且往下流。我們偶然得知液滴能在移動表面上維持球型並懸浮數分鐘[1],故設計實驗探討物理機制。設計出能高速旋轉且維持穩定的滾筒,是首要克服的關鍵;而為了解液滴轉動行為,我們學會操作粒子圖像測速法。此研究控制參數包括滾筒轉速、液滴半徑及種類,除了指出過去文獻未討論的重要細節,並嘗試建立解釋此運動行為的物理模型及推導方程式,得到簡單的解析解和物理圖像。 實驗上,相較在靜止液面只懸浮0.27秒,矽油滴在穩定移動表面可懸浮數分鐘,此可用文獻[2, 3]中的「空氣墊現象」解釋。移動表面上穩定懸浮的液滴,傾斜角θ與滾筒切線速度v及液滴半徑r的-2次方呈正比,實驗數據與我們的預測皆相符。液體種類影響懸浮的最低轉速,液滴受的交互作用力也因液體種類而異。未來將分析液滴晃動程度、可保持懸浮的速度區間與液滴半徑之關係。

Studies of spatial self-phase modulation of the laser beam passing through the olive oil

橄欖油含有葉綠素a,葉綠素b,和胡蘿蔔素等高熱吸收率的物質;高斯光束照射橄欖油時,橄欖油吸收的熱量,使橄欖油產生溫度梯度和折射率梯度,並產生熱透鏡(Thermal lens)和自調相(Self-phase modulation)現象。 以雷射光照射盛橄欖油水平置放的方型盒時,中央軸的照度最大,橄欖油的溫度最高,折射率和密度最小。由於對流作用的影響,使得光束照射到的橄欖油的上半部折射率梯度小於下半部;光束通過橄欖油後,在屏幕上出現的繞射圖樣呈現上半部的亮帶半徑小於下半部。 將橄欖油改置圓柱筒中,雷射光由上向下照射,可以消除熱對流現象。用不同功率的雷射,照射不同液柱高度,和不同熱吸收率的橄欖油;探討功率、液柱高度、和熱吸收率對:繞射亮帶最大半徑、繞射亮帶半徑隨時間的變化、和亮帶數目的影響。