Aptamer, 適體

(Source：Wikipedia) (存參)

Aptamer, 適體 (源自拉丁文「aptus」表示」適合」的意思,和希臘文「meros」表示」部位」的意思)是指與特定的目標分子結合的寡聚核酸或是 肽鏈。適體常常從大量的隨機序列被挑選出來,但自然的適體依舊存在如核糖開關中。適體可以用在學術研究亦可以當作大分子藥物應用在臨床診斷上。在適體的目標分子存在的情況下，適體能與核酶結合並進行自我剪切的動作，這些複合物能應用在研究、工業與臨床診斷上。

有高度專一性的適體能如下分類:

• DNA or RNA or XNA構成的適體(適體核酸);由寡核酸構成。
• 肽鏈構成的適體(適體肽鏈);由可變的多肽區域與蛋白質的兩端結合而成。

Aptamers (from the Latin aptus - fit, and Greek meros - part) are oligonucleotide or peptide molecules that bind to a specific target molecule. Aptamers are usually created by selecting them from a large random sequence pool, but natural aptamers also exist in riboswitches. Aptamers can be used for both basic research and clinical purposes as macromolecular drugs. Aptamers can be combined with ribozymes to self-cleave in the presence of their target molecule. These compound molecules have additional research, industrial and clinical applications.

More specifically, aptamers can be classified as:

• DNA or RNA or XNA aptamers. They consist of (usually short) strands of oligonucleotides.
• Peptide aptamers. They consist of one (or more) short variable peptide domains, attached at both ends to a protein scaffold.

楊氏模數---Young's modulus

(Source ：Wikipedia) (備存)


定義：

楊氏模量，也稱楊氏模數（英語：Young's modulus），是材料力學中的名詞。彈性材料承受正向應力時會產生正向應變，在形變量沒有超過對應材料的一定彈性限度時，定義正向應力與正向應變的比值為這種材料的楊氏模量。公式記為

${\displaystyle E={\frac {\sigma }{\epsilon }}}$

其中，${\displaystyle E}$ 表示楊氏模量，${\displaystyle \sigma }$ 表示正向應力，${\displaystyle \epsilon }$ 表示正向應變。

where

E is the Young's modulus (modulus of elasticity)

F is the force exerted on an object under tension;

A₀ is the actual cross-sectional area through which the force is applied;

ΔL is the amount by which the length of the object changes;

L₀ is the original length of the object.

楊氏模量以英國科學家托馬斯·楊命名。

Young's modulus, also known as the elastic modulus, is a measure of the stiffness of a solid material. It is a mechanical property of linear elastic solid materials. It defines the relationship between stress (force per unit area) and strain (proportional deformation) in a material. Young's modulus is named after the 19th-century British scientist Thomas Young. However, the concept was developed in 1727 by Leonhard Euler, and the first experiments that used the concept of Young's modulus in its current form were performed by the Italian scientist Giordano Riccati in 1782, pre-dating Young's work by 25 years.^[1] The term modulus is the diminutive of the Latin term modus which means measure.

A solid material will deform when a load is applied to it. If it returns to its original shape after the load is removed, this is called elastic deformation. In the range where the ratio between load and deformation remains constant, the stress-strain curve is linear. Not many materials are linear and elastic beyond a small amount of deformation. A stiff material needs more force to deform compared to a soft material, and an infinite force would be needed to deform a perfectly rigid material, implying that it would have an infinite Young's modulus. Although such a material cannot exist, a material with a very high Young's modulus can be approximated as rigid.^[2]

Material stiffness should not be confused with:

• Strength: the strength of material is the amount of force it can withstand and still recover its original shape;
• Geometric stiffness: the geometric stiffness depends on shape, e.g. the stiffness of an I beam is much higher than that of a round tube made of the same steel, thus having the same rigidity, and same mass of material per length;
• Hardness: the hardness of a material defines the relative resistance that its surface imposes against the penetration of a harder body;
• Toughness: toughness is the amount of energy that a material can absorb before fracturing.