Breakpoint

The concentration at which micellization commences is called the critical micelle concentration, erne. Any experimental teclmique sensitive to a solution property modified by micellization or sensitive to some probe (molecule or ion) property modified by micellization is generally adequate to quantitatively estimate the onset of micellization. The detennination of erne is usually done by plotting the experimentally measured property or response as a hmction of the logarithm of the surfactant concentration. The intersection of asymptotes fitted to the experimental data or as a breakpoint in the experimental data denotes the erne. A partial listing of experimental... 

Next, an equation for a test statistic is written, and the test statistic s critical value is found from an appropriate table. This critical value defines the breakpoint between values of the test statistic for which the null hypothesis will be retained or rejected. The test statistic is calculated from the data, compared with the critical value, and the null hypothesis is either rejected or retained. Finally, the result of the significance test is used to answer the original question. 

For a wide-hoiling-range material such as cmde oil, the boiling point is taken as an average of the five temperatures at which 10, 30, 50, 70, and 90% of the material is vaporized. A highly paraffinic cmde oil can have a characterization factor as high as 13, whereas a highly naphthenic cmde oil can be as low as 10.5, and the breakpoint between the two types of cmde oil is approximately 12. 

Reductive alkylations and aminations requite pressure-rated reaction vessels and hiUy contained and blanketed support equipment. Nitrile hydrogenations are similar in thein requirements. Arylamine hydrogenations have historically required very high pressure vessel materials of constmction. A nominal breakpoint of 8 MPa (- 1200 psi) requites yet heavier wall constmction and correspondingly more expensive hydrogen pressurization. Heat transfer must be adequate, for the heat of reaction in arylamine ring reduction is - 50 kJ/mol (12 kcal/mol) (59). Solvents employed to maintain catalyst activity and improve heat-transfer efficiency reduce effective hydrogen partial pressures and requite fractionation from product and recycle to prove cost-effective. 

During superchlorination or shock treatment, ammonium ion is oxidized to nitrogen by breakpoint chlorination which is represented by the simplified reaction sequence... 

In reahty the chemistry of breakpoint chlorination is much more complex and has been modeled by computer (21). Conversion of NH/ to monochloramine is rapid and causes an essentially linear increase in CAC with chlorine dosage. Further addition of chlorine results in formation of unstable dichloramine which decomposes to N2 thereby causing a reduction in CAC (22). At breakpoint, the process is essentially complete, and further addition of chlorine causes an equivalent linear increase in free available chlorine. Small concentrations of combined chlorine remaining beyond breakpoint are due primarily to organic chloramines. Breakpoint occurs slightly above the theoretical C1 N ratio (1.75 vs 1.5) because of competitive oxidation of NH/ to nitrate ion. Organic matter consumes chlorine and its oxidation also increases the breakpoint chlorine demand. Cyanuric acid does not interfere with breakpoint chlorination (23). 

Some nitrate is also formed, thus the HOCl/NH stoichiometry is greater than theoretical, ie, - 1.7. This reaction, commonly called breakpoint chlorination, involves intermediate formation of unstable dichloramine and has been modeled kinetically (28). Hypobromous acid also oxidizes ammonia via the breakpoint reaction (29). The reaction is virtually quantitative in the presence of excess HOBr. In the case of chlorine, Htde or no decomposition of NH occurs until essentially complete conversion to monochloramine. In contrast, oxidation of NH commences immediately with HOBr because equihbrium concentrations of NH2Br and NHBr2 are formed initially. As a result, the typical hump in the breakpoint curve is much lower than in the case of chlorine. 

The efficiency of most adsorbers is very near 100% at the beginning of operation and remains extremely high until a breakpoint occurs when the adsorbent becomes saturated with adsorbate. It is at the breakpoint that the adsorber should be renewed or regenerated. This is shown graphically in Fig. 29-11. 

Industrial adsorption systems are engineered so that they operate in the region before the breakpoint and are continually regenerated by units. 

Residuals of chloramine decline to a minimum value that is referred to as the breakpoint. When dosages exceed the breakpoint, free chloride residuals result. Breakpoint curves are unique for different water samples since the chlorine demand... 

BeckerK, HohoffC, SuhmittB, Christen HJ, NeubauerBA, Sandrieser T, Becker CM (2006) Identification of the microdeletion breakpoint in a GLRA1 null allele of Turkish hyperekplexia patients. Hum Mutat 27 1061-1062... 

Microbial Resistance to Drugs. Figure 1 MlC-distribution showing the number of isolates of one species with a certain MIC. Some bacterial species are naturally resistant (intrinsic resistance) to drugs because their natural MIC is above the breakpoint. Naturally sensitive isolates as well as naturally resistant ones can acquire resistance and with that increase their MIC (acquired or secondary resistance). 

In chronic myelogenous leukemia (CML) as well as in a subset of acute lymphoblastic leukemia (ALL) Bcr-Abl, a fusion protein of c-Abl and the breakpoint cluster region (bcr), is expressed in the cytosol of leukemic cells. This fusion protein forms homo-oligomeric complexes that display elevated kinase activity and is the causative molecular abnormality in CML and certain ALL. The transforming effect of Bcr-Abl is mediated by numerous downstream signaling pathways, including protein kinase C (PKC), Ras-Raf-ERK MAPK, JAK-STAT (see below), and PI3-kinase pathways. 

FIG. 2 Low-frequency conductivity at 45°C as a function of composition, a (weight fraction decane relative to decane and brine) for brine, decane, and AOT microemulsions exhibiting the phase behavior illustrated in Fig. 1. The breakpoint at a = 0.85 corresponds to the onset of percolation. This conductivity increases by two orders as a decreases from 0.85 to 0.7. (Reproduced by permission of the American Institute of Physics from Ref. 37.)... 

Water proton self-diffusion exhibits a break point and begins to increase at a = 0.85. In the case of AOT self-diffusion, a breakpoint also occurs, but AOT self-diffusion continues to slow as a decreases further. These breakpoints in both water and AOT selfdiffusion behavior at a = 0.85 coincide with the breakpoint in electrical conductivity illustrated in Fig. 1, where the onset of electrical conductivity percolation occurs. At a = 0.7 two more breakpoints in the water proton and AOT self-diffusion are seen. Water proton self-diffusion increases more markedly and AOT self-diffusion beings to increase markedly. 

FIG. 5 Order parameter for disperse pseudophase water (percolating clusters versus isolated swollen micelles and nonpercolating clusters) derived from self-diffusion data for brine, decane, and AOT microemulsion system of single-phase region illustrated in Fig. 1. The a and arrow denote the onset of percolation in low-frequency conductivity and a breakpoint in water self-diffusion increase. The other arrow (b) indicates where AOT self-diffusion begins to increase. 

FIG. 9 Measured self-diffusion coefficients at 25°C for toluene (A), water ( ), acrylamide ( , and AOT ( ) in water, toluene, and AOT reverse microemulsions as a function of cosurfactant (acrylamide) concentration, f (wt%). The breakpoint at about 1.2% acrylamide approximately denotes, the onset of percolation in electrical conductivity. 

A toxic propylene glycol plasma level breakpoint remains to be determined. 

Development of resistance to P -lactam antibiotics, including penicillins and cephalosporins, has significantly impacted the management of bacterial meningitis. Approximately 17% of United States pneumococcal CSF isolates are resistant to penicillin, and 3.5% of CSF isolates are resistant to cephalosporins.26 The Clinical and Laboratory Standards Institute (CLSI) has set a lower ceftriaxone susceptibility breakpoint for pneumococcal CSF isolates (1 mg/L) than for isolates from non-CNS sites (2 mg/L). Increasing pneumococcal resistance to penicillin G... 

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