Critical Concentration Ratio Research Articles

Interactions between Poly(ethylene oxide) and Sodium Alkylcarboxylates As Studied by Conductivity and Gel Permeation Chromatography

The interactions between PEO and sodium alkylcarboxylates (octyl, decyl, and dodecyl) have been investigated by conductivity measurements and gel permeation chromatography (GPC). Also included in the study was sodium dodecyl sulfate. From the conductivity measurements the critical aggregation concentration, ionization degree, and binding ratios were determined; the binding ratio was also determined from GPC. PEO–surfactant interactions were observed for all the studied surfactants, except sodium octanoate. For the polymer–surfactant complexes the ionization degree was in all cases observed to be about 0.2 higher than the ionization degree for the corresponding aqueous micelles. Further, the binding ratio decreased somewhat with decreasing chain length of the alkylcarboxylate. The Gibbs free energy showed that the polymer–surfactant interaction decreases with decreasing chain length of the alkylcarboxylates and is weaker for alkylcarboxylate compared to alkylsulfate of similar chain length.

Ion dynamics in the sheath in multicomponent plasma with negative ions

Observations on steady state ion-rich sheath around a negatively biased grid in a double plasma device have been made in multicomponent plasma with negative ions. A hump in the potential profile is found to occur at the sheath edge. The characteristics of the hump depend on the grid voltage, source biasing voltage, density difference in the two chambers, and the negative to positive ion concentration ratio. It is argued that resonance which is coupled with the beam ions and background ions is associated in the excitation mechanism to create the nonsymmetrical structures in the plasma potential profile. Below the critical concentration ratio, the hump grows in height and above the critical ratio, the width of the hump increases but the height decreases and ultimately it vanishes. The variation in the hump potential profile due to the injection of negative ions can be explained by the ion momentum exchange and by their dynamics.

Cometabolic degradation of chlorophenols by Acinetobacter species

Phenol-induced cells of Acinetobacter species were used to degrade 4- and 3-chlorophenols (CP). Several different patterns of batch 4- or 3-CP degradation were shown by cultures growing in different concentration ratios of phenol (growth substrate) to 4- or 3-CP, e.g. complete degradation of 4- or 3-CP at the depletion of phenol, partial 4- or 3-CP degradation at the depletion of phenol and inhibition of both phenol and 3-CP degradations. These patterns are characteristics of concentration-dependent substrate competition/inhibition between phenol and CP. As the initial concentration ratio of phenol/4-CP reduced, decreasing values of the cell growth yield were obtained from each batch experiment. Two different values of a critical concentration ratio were necessary to completely degrade 4- and 3-CP in the presence of phenol; below these ratios, the initial amount of 4- or 3-CP was only partially degraded. The 3-CP transformation product toxicity, as opposed to the absence in phenol/4-CP, might have accounted for the requirement of a higher critical phenol/3-CP concentration ratio than that for phenol/4-CP. Furthermore, higher COD accumulation (2.38 mg COD mg −1 3-CP vs 1.27 mg COD mg −1 4-CP) but less chloride release (0.13 mg Cl − mg −1 3-CP vs 0.26 mg Cl − mg −1 4-CP) was obtained in phenol/3-CP experiments. These results suggest that the cometabolic degradation pathways for 4- and 3-CP may differ at the monooxygenation step such that the overt 3-CP transformation product toxicity could be attributed to accumulation and autopolymerization of 3-chlorocatechol.

Clay Swelling Diagrams: Their Applications in Formation Damage Control

Abstract A novel method has been developed to quantify clay swelling in aqueous solutions. In this method, a swelling clay is dispersed into an aqueous solution of desired composition, and then mounted in a special cell for X-ray diffraction (XRD) analysis. Using this method, the effects of solution pH, salinity, cation composition, temperature, fluid pressure, and overburden pressure on clay swelling can all be determined efficiently. This method uses only a small amount of sample and offers some advantages over the conventional coreflood method. It can also be used to evaluate the performance of clay stabilizers. We have determined the critical salt concentration (CSC) and critical cation ratio (e.g., Na/Ca, Na/K) for macroscopic osmotic swelling of the most common swelling clays. The information can be represented by a set of swelling diagrams in which the solution composition responsible for osmotic swelling and formation damage is delineated. The swelling diagrams can be used to determine the compatibility between shales and drilling fluids, between swelling clays and drilling filtrate or completion fluids, and between swelling clays and flooding fluids used in EOR. The effects of temperature and pressure on clay swelling have also been quantified using this method. Temperature has a small effect on clay swelling between 20-100°C; but the differential pressure between the overburden and fluid pressures (Po - Pf) has a significant effect on clay swelling. The greater the differential pressure, the less the clay swells. The important implications of these results on petroleum drilling and production will be discussed. It should be cautioned that the swelling diagrams can not be applied to fines migration problems associated with non-swelling clays such as kaolinite and illite.

Is there more than one critical concentration ratio? An empirical test for the Portland cement industry

Past attempts to estimate the critical concentration ratio maintained the hypothesis of only two structural groupings: competitive versus non-competitive. In view of the spectrum of competitive conduct allowed by oligopoly theory, the validity of the two groupings is restrictive and should be tested. Using data from the Portland cement industry, this paper conducts such a test, employing a non-linear switching regression technique based on the logistic function. The hypothesis of two structural groupings is not rejected.

Effect of ceramic plant effluent on phenol degradation by Acinetobacter calcoaceticus

Phenol-induced cells of Acinetobacter species were used to degrade 4- and 3-chlorophenols (CP). Several different patterns of batch 4- or 3-CP degradation were shown by cultures growing in different concentration ratios of phenol (growth substrate) to 4- or 3-CP, e.g. complete degradation of 4- or 3-CP at the depletion of phenol, partial 4- or 3-CP degradation at the depletion of phenol and inhibition of both phenol and 3-CP degradations. These patterns are characteristics of concentration-dependent substrate competition/inhibition between phenol and CP. As the initial concentration ratio of phenol/4-CP reduced, decreasing values of the cell growth yield were obtained from each batch experiment. Two different values of a critical concentration ratio were necessary to completely degrade 4- and 3-CP in the presence of phenol; below these ratios, the initial amount of 4- or 3-CP was only partially degraded. The 3-CP transformation product toxicity, as opposed to the absence in phenol/4-CP, might have accounted for the requirement of a higher critical phenol/3-CP concentration ratio than that for phenol/4-CP. Furthermore, higher COD accumulation (2.38 mg COD mg−1 3-CP vs 1.27 mg COD mg−1 4-CP) but less chloride release (0.13 mg Cl− mg−1 3-CP vs 0.26 mg Cl− mg−1 4-CP) was obtained in phenol/3-CP experiments. These results suggest that the cometabolic degradation pathways for 4- and 3-CP may differ at the monooxygenation step such that the overt 3-CP transformation product toxicity could be attributed to accumulation and autopolymerization of 3-chlorocatechol.

Increased level of cytokinin ribosides in jasmonic acid‐treated potato (Solanum tuberosum) stem node cultures

Cytokinin free bases, ribosides and 9‐glucosides were measured in stem node cultures of potato (Solanum tuberosum L. cv. Ulster Sceptre) in the presence or absence of 1 μM jasmonic acid (JA) to examine whether or not their changed levels were part of the JA‐induced growth response. The enhanced growth response in JA‐treated plantlets included: expanded root systems, extended leaf areas, increased number of nodes, and enlarged stem diameters. The protein analysis revealed a substantial decrease in a 62‐kDa polypeptide. On a dry weight basis, the levels of ribulose‐1,5‐biphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) and chlorophylls a and b were constant. The total concentration of endogenous cytokinins remained virtually the same in control and treated plantlets; but in JA‐treated plantlets the amount of cytokinin free bases and cytokinin 9‐glucosides decreased. In addition, the level of cytokinin ribosides was elevated. The ratio between active and inactive cytokinins increased from 1.2 to 2.1, which correlates with the enhanced growth of potato plantlets grown on 1 μM JA. Thus the observed growth and developmental changes may be a consequence of the measured altered cytokinin level. However, significant morphological alterations of the potato plantlets treated with JA may also be a result of the changed critical cytokinin concentration or critical ratios of cytokinins to auxins and JA, rather than their absolute concentrations.

Origin of the Grain Growth Anomaly in Donor-Doped Barium Titanate

The grain growth of donor-doped BaTiO3 prepared from powders with different initial specific surface areas was investigated, and a microscale model was proposed that relates the critical amount of donor-dopant, which inhibits anomalous grain growth, to the critical free surface area at the phase boundary. The results show that the model proposed can explain the inhibition of anomalous grain growth in donor-doped BaTiO3 and can predict well the ratio of critical concentration to surface area for the system studied.

Voltage Step Characteristics of Oxygen Concentration Cell Sensors for Nonequilibrium Gas Mixtures

Concentration cell zirconia oxygen sensors show steady‐state output characteristics having an abrupt voltage step at critical oxygen combustible gas concentration ratio. The voltage step characteristics were investigated experimentally at various temperatures using simple gas mixtures containing oxygen and combustible gas. Experimental results indicated that there are three temperature regions for the voltage step characteristics: (i) a high temperature region (region I) in which the voltage step occurs near the stoichiometric composition. This results from equilibrium reaction occurring in the gas mixtures; (ii) a middle temperature region (region II) in which the voltage step deviates from the stoichiometric composition of the nonequilibrium gas mixtures. The magnitude of the deviation does not depend on temperature; (iii) a low temperature region (region III) in which the voltage characteristics strongly depend on temperature. In the region II , the magnitude of the deviation in the voltage step characteristics is somewhat influenced by the flow rates of the gas mixtures and the thickness of a porous coating on the sensor electrode for protection. This behavior of the sensor was analyzed by a kinetic model in which the sensor electrode is assumed to have a high catalytic activity for the reaction of the combustible gas and oxygen. The model also considers mass transport through the porous coating and gaseous boundary layers. The sensor characteristics in the region II , in which the sensors are mainly used in practice, can be explained by this model.

The Search for a Critical Concentration Revisited

This paper examines the issue of whether there is a four-firm critical concentration ratio above which industries earn supranormal profits. A statistical test is employed to investigate the functional stability of the estimated relationship. Although the initial results indicate a range in the concentration ratio of between 0.48 and 0.55 over which the functional relationship destabilizes, additional analysis fails to identify a clear break in the concentration-profitability relationship. It can only be concluded that a critical concentration does not appear to exist.

The Critical Choice Between the Concentration Ratio and the H-Index in Assessing Industry Performance

The paper shows that in addition to the theoretical relevance of choosing between the Hirschman-Herfindahl index and the concentration ratio, both measures may provide empirically very different information to assess industry performance. It is shown that the correspondence between the two measures can be represented by a horn-shaped figure. The implications of this horn-shaped relationship are investigated in the context of specifying empirical profitability-concentration models. Among different specification effects tested, it is shown that the neglect of the hornrelationship may bias the results towards the identification of a critical concentration ratio.

Testing the interaction between concentration and barriers to entry

Various functional forms are employed to examine the independent and interactive effects of seller concentration and entry conditions on profitability. Significant interactive effects appear. There is also some evidence of a critical concentration ratio, which affects the slope of the concentration-profitability relationship.

Self-focusing of powerful CO_2-laser beams in collisional plasmas

The self-focusing phenomenon of powerful Gaussian CO2-laser beams in collisional plasmas is analyzed using a new technique based on geometrical optics. The problem of self-focusing is reduced to a nonlinear differential equation in the beamwidth parameter, which is then numerically solved by using a computational technique and assuming that the laser beam and the plasma are either coupled or decoupled along the propagation path. The beamwidth parameter is, in general, a function of propagation distance, radial position, collisional-energy-loss to conduction-energy-loss ratio, initial beamwidth, laser power, and electron concentration to its critical-concentration ratio. The effect of variation of each of these parameters on the variation of the beamwidth parameter is investigated.

Concentration, Price, and Critical Concentration Ratios

A potentially important parameter that has not yet been convincingly estimated is the critical concentration ratio. This paper attempts to estimate it in three types of market. The estimation of a critical concentration ratio, if one exists, seems of potentially great importance because of its implication for antitrust policy. If a critical concentration ratio were found and if concentration had no effect below that level, it would seem to follow that a horizontal merger in a market where concentration was below the critical level and where the merger could not increase concentration to the critical level could not substantially lessen competition or tend to create monopoly.

Conversion of “Tables of Spectral-Line Intensities” for NBS copper arc into table for inductively coupled argon plasmas

This paper describes an approach used to convert the Tables of Spectral-Line Intensities for the copper arc explored by M eggers, C orliss and S cribner at the National Bureau of Standards (NBS Tables) into a table appropriate for inductively coupled plasmas (ICP). Previous work of this author was extended to determine “definitive” factors for converting the intensities listed in the NBS Tables into ICP sensitivities using the ICP detection limits of more than 800 prominent lines published by W inge, P eterson and F assel. A computer iteration procedure was devised to find simultaneously the desired conversion factors and the true relative intensity distribution in the background spectrum of the argon ICP explored by W inge et al. This approach proved to be viable and resulted in a complete translation of the tables for the NBS copper arc into a table of ICP sensitivities, which, together with a previously described approach by this author to quantify line coincidences in terms of critical concentration ratios, formed the basis of new Line Coincidence Tables for Inductively Coupled Plasma Atomic Emission Spectrometry involving 896 prominent lines of 67 elements. The Appendix of the present work produces a list of these prominent lines arranged according to element and wavelength, along with sensitivities, detection limits, and ratios of the detection limits to the best detection limit of the element. A second list of some 200 supplementary computer predicted prominent lines is also appended.

Spectral interference on the emission of sulphur I 180.73 nm in an inductively coupled plasma

Spectral interferences on the S I 180.73 nm emission line by Al, Ca, Mn and Fe in an inductively coupled plasma are described. The critical concentration ratios for Ca, Mn, Al and Fe with respect to S are 90, 300, 3300 and 25000 respectively (full width at half maximum = 0.0075 nm). Intensity measurements at various observation zones in the plasma show that the spectral interference from Ca and Mn emission line overlaps may be reduced by observing the S emission at a lower observation height in the plasma.

ICP: D.c. arc in a new jacket?

The starting-point of this article is the common problem encountered in both inductively coupled plasma atomic emission spectrometry (ICP—AES) and d.c. arc AES when used for trace analysis, namely the extraction of a true net analyte signal from the composite radiation observed in the spectral window of an analysis line. In this connection the author points, first, to the wealth of data available in the literature on d.c. arc spectrography, which again is of topical interest in the further development of ICP—AES, and second, to the lack of data on the relative intensities of spectral lines emitted for ICPs, which makes it difficult to choose reliable analysis lines when the matrix elements yield complex spectra. The main topic of the paper is the description of an approach currently under development at Philips Research Laboratories, the eventual goal of which is to arrive at a new tabulation of spectral interferences for ICP spectra. Essentially the previous experience in converting intensities from the NBS Tables of Spectral-Line Intensities into ICP sensitivities is extended to the prediction of the degree of spectral interference using (a) ICP sensitivity ratios of analysis and interfering lines, (b) concentration ratios of analytes and interferents, (c) wavelength distances between interfering and analysis lines, and (d) the spectral bandpass of the spectrometer. Computer programs have been written for a general-purpose approach and a specific approach. In the general-purpose approach, a tabulation is created which can be consulted for any set of conditions as dictated by the spectral apparatus, the sample composition and the analytes. However, the user of the table has to look up each item of interest and to make decisions. In the specific approach, all decisions are built into the computer program. The user only formulates the matrix and upper limits of concentrations and a set of analytes and their lower concentrations of interest, and the computer program provides a set of the most sensitive analysis lines that are interference free under the specified conditions and gives the reasons for disqualification of other sensitive lines. In the general purpose approach, the sensitivity ratios and concentration ratios are taken into account by the so-called “critical concentration ratio”, defined as the ratio of the concentrations of interferent to analyte at which the ratio of the intensities of interfering line to analysis line within the spectral window of the analysis line is equal to unity. Wavelength distance and spectral bandpass are involved through the calculation of the areas of the Voigt profiles of analysis and interfering lines that fall within a spectral window the width of which is equal to the full width at half maximum of the “average” spectral line in the ICP spectrum. A discussion on the assignment of an appropriate value to the a-parameter of the Voigt profile is included. In the specific approach, the majority of the procedures of the general-purpose approach are used. However, the program computes, instead of critical concentration ratios, the intensity ratios of interferent to analyte lines for the concentrations specified. Examples of both approaches are presented in tabular form. The present status of the work is reviewed, and envisaged projects including experimental verifications and extensions are discussed. Various gross errors inherent in the conversion of the intensities of the NBS Tables of Spectral-Line Intensities are pointed out. Results of the calculations are used to illustrate the effect of spectral resolution of the spectral interferences and conclusions with respect to the resolution of spectrometers and the number of spectral windows required in ICP—AES are drawn. Linking up with earlier work of other investigators, the author finally points to the necessity of using state-of-the-art spectrometers in order to circumvent the adverse effects of straylight on the detection limits. Experimental results obtained with a 10-years old monochromator illustrate the disastrous effect of scattered radiation which occurs not only with Ca and Mg as main components, but with all major constituents that yield line-rich spectra or spectra with very intense lines.

Oxygen precipitation in silicon

This paper presents the results of our observing oxygen precipitation in a silicon crystal at 1000 °C using infrared absorption, TEM, and x-ray techniques. Comparison of results shows excellent agreement between TEM and IR for the number of precipitate particles formed. TEM data show that the number of particles increases as the annealing time is increased for oxygen contents above a critical concentration ratio of about 4 (30 ppma at 1000 °C). The number of particles formed at lower ratios remains relatively small. Detailed analysis of the TEM results has yielded a relationship between precipitate volume and the total area of punched-out loops. These loops, however, account for only a small fraction of the silicon atoms displaced by the growing precipitates. X-ray results indicate the defects are of an interstitial nature, in agreement with TEM.

The Concentration-Profitability Relationship: Is There a Critical Concentration Ratio?

A MAJOR concern of the body of economic analysis surrounding the theory of the firm is whether the pricing behavior of oligopolistic industries differs from that of competitive industries. Theory suggests that where small groups of sellers account for a substantial proportion of an industry's output, the recognition of mutual interdependence will result in the absence of price competition. Furthermore, the prices and profits are expected to be above the level that would obtain under competitive conditions. Empirical investigations of the relationship between seller concentration and profitability have produced results generally in accord with the theory. However, neither theory nor the empirical evidence provides a clear insight into the specific nature of the concentration-profitability association. The unanswered question is whether or not there is a 'threshold' level of concentration which separates groups of industries earning significantly different profit rates. The purpose of this study is to examine empirically whether a dichotomous functional form of the concentration-profitability association presents a better explanation of the underlying relationship than the continuous linear form: and, if it does, how concentration and profitability are related within the separated groups. The results suggest that there is a critical value for concentration and that there is no significant association between concentration and profit rates within high and low concentration groups.

Protein-polynucleotide scattering centers as a protein structure probe

When certain basic globular proteins are mixed with nucleic acids near a critical concentration ratio, large, low density scattering centers of about 10 9 particle weight are created. Scattering from these complexes is altered when thermally inactivated proteins are substituted for enzymes in their native, globular conformation. Scattering data from heat-treated ribonuclease and lysozyme mixed with four different synthetic homopolyribonucleotides are reported. The concentration of nucleic acid necessary to produce maximum scattering from a heat-treated protein sample is shown to be a direct indication of the amount of enzyme that remains biologically active after being heated.