Roscoe surface

This result is similar to drained triaxial tests (namely, CTj = constant, dp = — (l/3)rfa(, dq= — da, dq/dp = 3). As shown in Fig. 6.2d, if an undrained stress path B-B under a consolidation pressure p g intersects with a drained stress path A-A" under a consolidation pressure a point C, the void ratio obtained from the undrained test is the same as the void ratio obtained from the drained test. We can draw these states in a space p, q, e) as illustrated in Fig.6.2f, which shows that the critical state is reached after travelling the surface referred to as the state boundary surface or Roscoe surface in both the undrained and drained tests. The line of failure is known as the critical state line (CSL). It is noted that the projection of CLS in the space p, q, e) onto the space (p, q) is given as = Mp, and the surface formed by CLS and its projection onto q, e) is referred to as Hvoslev surface, which is a failure surface found by Hvoslev in 1937 through a series of direct shear tests conducted on Vienna clay. 

Oxygen is not the only surface contaminant, but it is the most prevalent. Other frequent ones are sulfur (tarnish) and phosphorus. Sometimes a combination, such as chlorate (O + Cl), forms a layer. These effects are known collectively as the Roscoe Effect (Metzger and Read, 1958). 

STM has also been used to study the adsorption of large biomolecules on a surface in solution (Roscoe, 1996). However, caution must be exercised because of the tendency of the probe tip itself to push the biomolecule, Le., interfere with its own measurement. 

The study of surface behavior is not of recent origin. In the 1920s, Joffe (1928) observed an increase in the ductility in the presence of water on solid potassium chloride. In 1930s, Roscoe (1926) published that the presence of oxides on certain metals, such as cadmium, produced a surface hardening effect. 

Tejasari, D. 2007. Evaluation of Ginger (Zingiber officinale Roscoe) Bioactive Compounds in Increasing the Ratio of T-eell Surface Moleeules of CD3+CD4+ CD3+CD8+ In-Vitro. Malaysian Journal of nutrition, 13(2), 161-70. 

Omanovic, S. and Roscoe, S.G. (2000) Interfacial behavior of -lactoglobulin at a stainless steel surface an electrochemical impedance spectroscopy study. J. Colloid Interface ScL, 227,452-460. 

Roscoe, J.M., Abbatt, J.P.D. Diffuse reflectance FTIR study of the interaction of alumina surfaces with ozone and water vapor. J. Phys. Chtan. A 109, 9028-9034 (2005)... 

A series of studies was made by Roscoe and co-workers on the adsorption and electrochemical oxidation mechanisms of the amino acids glycine, a- and ) -alanine, and a-, and y-aminobutyric acid at a platinum electrode in order to determine the role that the position of the amino group plays in the surface adsorption properties and subsequent oxidation of these amino acids. The investigations were made in aqueous solutions at pH 1,7, and 13 using steady-state current-potential measure-... 

Figure 11. Surface charge density of j -lactoglobulin A at a platinum electrode with an anodic end potential of 1.0 V (vs. SCE) versus the concentration (w/v) of the protein in phosphate buffer (299 K) at pH 2.0 (a). 6.0 (a), 7.0 (o). 8.0 ( ), and 11.0 ( ). (Reprinted from Roscoe...

At pH 7.0, Roscoe et al found that surface adsorption as measured by surface charge density was at the minimum value. This may be due partly to an increase in the volume of the )8-lactoglobulin structure during this denaturation from the compact globular structures at the lower pHs, resulting in a smaller packing density and hence decreased surface concentration. At pH 8.0, their experimental results showed an increase in the... 

Heat affects the conformation of proteins, and most proteins undergo fairly rapid heat denaturation somewhere between 333 and 363 A series of experiments was made by Roscoe and Fuller in which the surface adsorption behavior of bovine )8-lactoglobulin A, hen egg-white lysozyme and bovine pancreatic ribonuclease A was studied at a platinum electrode as a function of temperature using cyclic voltammetry. The protein solution and the electrochemical cell were separately immersed in the thermostated bath and allowed to equilibrate for 30 mins. The protein... 

Figure 18. Plots of the logarithm of surface charge density of jff-lac-toglobulin A (0.05 g 1 in phosphate buffer, pH 7.0) at a platinum electrode versus ( ) and of % free sulfhydryl versus fra )9-lactoglobulin heated at the s cified ten )erature f( r 30 min (o). (Reprinted from Roscoe el al, with permission.)...

Figure 24. Surface charge density,of protein at a platinum electrode versus the time of potential sweeping after the electrode was dipped in protein solution(s) in phosphate buffer (pH 7.0,368 K) and measured at 273 K. , dipped in a /c-casein solution (0.13 g r ) A, dipped first in the K-casein solution and then in a -lactoglobulin solution (0.16 g 1" 2 min dip each v, dipped first in the /c-casein solution followed by the jff-lactoglobulin solution, 8 min dip each , dipped first in the )ff-lactoglobulin solution followed by the /c-casein solution, 2 min dip each O, dipped first in the J -lactoglobulin solution followed by the /c-casein solution, 8 min dip each. (Reprinted from Roscoe and Fuller with permission.)...

Figure 25. Surface charge density, Cads adsorbed milk at a platinum electrode versus the time of potential sweeping (-0.75 to 1.0 V vs. SCE) in phosphate buffer (pH 7.0) after the electrode was dipped in unpasteurized milk for 16 min at 363 K and measured at 363 K, 299 K, a and 273 K, a. (Reprinted from Roscoe and Fuller with permission.)...

Sharon Roscoe s article is about protein surfaces and, in the views of the editors, is a classic in the sense that it works out some of the consequences of considering proteins as electrodes. This opens up, of course, an area of biochemistry which may allow an enhanced understanding of many phenomena which have proved difficult to rationalize. 

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