Comparative study between the fracture stress of poly- and single-crystalline graphene using a novel nanoelectromechanical system structure

Micro & nano letters

article

Jimmy Ng¹  Qi Chen²  Ya-Hong Xie¹  Albert Wang²  Tianru Wu³ 

[1] Department of Materials Science and Engineering, University of California Los Angeles;Department of Electrical and Computer Engineering, University of California Riverside;State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystems and Information Technology, Chinese Academy of Sciences

关键词: fracture;    graphene;    grain boundaries;    monolayers;    chemical vapour deposition;    graphene devices;    nanoelectromechanical devices;    fracture stress;    polycrystalline graphene;    single-crystalline graphene;    two-dimensional carbon material;    mechanical properties;    grain boundaries;    monolayer graphene;    novel nanoelectromechanical system structure;    suspended graphene ribbon devices;    electrostatical actuation;    graphene sheet;    nail structures;    electromechanical responses;    hnite element simulations;    novel NEMS structure;    chemical vapour deposition;    local feeding CVD;    C;   

DOI  :  10.1049/mnl.2017.0422

学科分类：计算机科学（综合）

来源: Wiley

【 摘 要 】

Landmark advancements in the clinical diagnosis and treatment of acid base disturbances have included the Henderson-Hasselbalch equation (1916), base excess (1960), anion gap (1970) and the strong ion approach (1983). The Henderson-Hasselbalch equation used the pH value as an overall measure of acid base status, PCO2 as an independent measure of the respiratory component of acid base balance and base excess, and actual bicarbonate concentration or standard bicarbonate as a measure of the metabolic (also called non respiratory) component of acid base balance. However it only provides an estimate of the magnitude of a metabolic acidosis and not the mechanism of its development. Hyperchloremic acidosis is one of many such clinical conditions that have no rational explanation. It is well recognized that the rapid infusion of large quantities of 0.9% NaCl induces acidosis and decreases plasma bicarbonate concentration1. Stewart proposed that plasma pH was determined by three independent factors; PCO2, the strong ion difference (SID), which is the difference between the charge of plasma strong cations (sodium, potassium, calcium and magnesium) and the anions (chloride, lactate, sulfate, ketoacids, nonesterified fatty acids, fatty acids and many others) and Atot, which is the total plasma concentration of nonvolatile buffers (albumin, globulins, and inorganic phosphate)2. In this context, pH value and bicarbonate concentration are dependent variables and PCO2, SID and Atot are independent variables. Independent variables cannot be affected by changes within the system or by changes in other independent variables. In contrast, dependent variables are influenced directly and predictably by changes in the independent variables. From the three independent factors Stewart developed a complicated polynomial equation that expressed the pH value as a function of eight factors2. Subsequently this was simplified to six factors in 19973. The equation states the pH value is a function of three independent factors (PCO2, SID and Atot) and three constants (S, the apparent dissociation constant for plasma carbonic acid K1 and Ka the effective dissociation constant for nonvolatile buffers in plasma). pH = pK1 + log SID – Atot / (1 + 10pka-pH) S PCO2 The strong ion approach distinguishes six primary acid base disturbances (respiratory, strong ion, or nonvolatile buffer acidosis or alkalosis) instead of the four primary acid base disturbances (respiratory or metabolic acidosis and alkalosis) differentiated by the traditional Henderson Hasselbalch equation. Acidosis results from an increase in PCO2, nonvolatile buffer concentration (albumin, globulin and phosphate) or from a decrease in SID. Alkalosis results from decrease in PCO2 and nonvolatile buffer concentration or from an increase in SID. The strong ion approach provides an explanation for the development of hyperchloremic acidosis and therefore a rational treatment for this condition. Normal human plasma SID is 42 meq/l4, whereas the SID of 0.9% NaCl is 0 meq/l because sodium and chloride are both strong ions3. Administration of a large volume of 0.9% NaCl must, therefore decrease plasma SID which will create a strong ion acidosis (assuming that infusion does not cause a change in PCO2, plasma albumin globulin or phosphate concentrations). According to the traditional Henderson Hasselbalch equation hyperchloremic acidosis should be treated with sodium bicarbonate because the bicarbonate concentration was decreased. In contrast, the strong ion approach indicated that hyperchloremic acidosis was caused by the decrease in plasma SID and it is best treated by administering a solution with a high SID, such as sodium bicarbonate (SID 130 meq/l)5. Clinical guidelines indicate that at a normal pH value (7.4) a 1 meq/l decrease in SID will decrease the pH value by 0.016, a 1 mmHg increase in PCO2 will decrease the pH value by 0.009 and a 1 g/dl increase in total protein concentration will decrease the pH value by 0.039. A clinically important problem in sick patients is identifying and quantifying the presence of strong anions or cations in plasma that are not routinely measured. Unmeasured strong anion or cation concentration can be quantified by calculating the anion gap6. In summary the strong ion approach provides the clinician with an improved understanding of complex acid base disturbances and the mechanism of their development. This will help in more targeted treatments of acid base and electrolyte disorders. REFERENCES Moon M, Kramer G.C. Hypertonic saline dextran resuscitation from haemorrhagic shock induces transient mixed acidosis. Critical Care Medicine 1995; 23: 323-31. Stewart P.A. Modern quantitative acid base chemistry. Can Journal of Physiology and Pharmacology. 1983; 61: 1444-61. Constable P.D. A simplified strong ion model for acid base equilibrium. An application to horse plasma. Journal of Applied Physiology. 1997; 83: 297-311. Singer R.B, Hastings A.B. An improved clinical method for the estimation of disturbances of the acid base balance of human blood. Medicine 1948; 27: 223-42. Rehm M, Finsterer U. Treating intraoperative hyperchloremic acidosis with sodium bicarbonate or Tris-Hydroxymethyl Aminomethane (THAM). A randomized prospective study. Anasesthesia and Analgesia 2003; 96: 1201-8. Oh M.S, Carroll H.J. Current concepts in the anion gap. New England Journal of Medicine 1977; 297: 814-7.

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