Allowance For Effects Research Articles

Interpretation of thermodynamic non-ideality in sedimentation equilibrium experiments on proteins

This investigation re-examines theoretical aspects of the allowance for effects of thermodynamic non-ideality on the sedimentation equilibrium distribution for a single macromolecular solute, and thereby resolves the question of the constraints that pertain to the definition of the activity coefficient term in the basic sedimentation equilibrium expression. Sedimentation equilibrium results for ovalbumin are then presented to illustrate a simple procedure for evaluating the net charge (valence) of a protein from the magnitude of the second virial coefficient in situations where the effective radius of the protein can be assigned. Finally, published sedimentation equilibrium results on lysozyme are reanalysed to demonstrate the feasibility of employing the dependence of the second virial coefficient upon ionic strength to evaluate both the valence and the effective radius of the non-interacting solute.

Allowance for effects due to thermoelectrically induced vortex motion in an analysis of structure formation on melt surfaces

A model of thermoelectrically induced formation of surface periodic structures allowing for vortex motion of the melt is proposed. An analytical solution for surface profile dynamics involving two-dimensional transport is obtained. It is shown that structure formation can occur only when the melt viscosity is sufficiently low.

Buckling of Tapered Circular Plates: Allowances for Effects of Shear and Radial Deformation*

ABSTRACT Elastic axisymmeiric buckling of tapered circular plates under a compressive radial load is analyzed. The effects of shear and prebuckling radial deformation are considered in the analysis because they are important when plates are thick. No previous buckling data are known to exist for tapered circular plates with allowance for both of these effects. The buckling analysis is performed using the Rayleigh-Ritz method. The shooting method is used in the computation of the varying stress function along the plate radius. Comprehensive generic buckling results for circular plates with linearly or parabolically varying thickness are presented. It is noted that shear deformation tends to reduce the buckling load. However, this reduction in buckling load is somewhat offset by the strength-enhancing effect of prebuckling radial deformation that is smaller but of the same order of magnitude. Optimal taper parameter values for such tapered plates are obtained. It is found that the optimal taper is insensiti...

Acquisition and processing of data for isotope-ratio-monitoring mass spectrometry

Methods are described for continuous monitoring of signals required for precise analyses of 13C, 18O, and 15N in gas streams containing varying quantities of CO 2 and N 2. The quantitative resolution (i.e. maximum performance in the absence of random errors) of these methods is adequate for determination of isotope ratios with an uncertainty of one part in 10 5; the precision actually obtained is often better than one part in 10 4. This report describes data-processing operations including definition of beginning and ending points of chromatographic peaks and quantitation of background levels, allowance for effects of chromatographic separation of isotopically substituted species, integration of signals related to specific masses, correction for effects of mass discrimination, recognition of drifts in mass spectrometer performance, and calculation of isotopic δ values. Characteristics of a system allowing off-line revision of parameters used in data reduction are described and an algorithm for identification of background levels in complex chromatograms is outlined. Effects of imperfect chromatographic resolution are demonstrated and discussed and an approach to deconvolution of signals from coeluting substances described.

Allowance for effects of electrostatic repulsion on protein dimerization

A simple procedure for assessing the extent of electrostatic effects on protein dimerization is described and illustrated by application to published results on the ionic strength dependence of the dimerization constant for α-chymotrypsin at pH 4 (Aune, K.C., Goldsmith, L.C. and Timasheff, S.N. (1971) Biochemistry 10, 1617–1622). From the analysis it is concluded that the inverse dependence of α-chymotrypsin dimerization upon ionic strength is predominantly a general electrostatic effect, rather than a consequence of repulsion between two specific charged residues on the adjacent monomers comprising dimer.

Further probes into quantitative aspects of competitive binding assays: Allowance for effects of antigen multivalency in immunoassays

Effects of antigen multivalency on procedures for the analysis of immunoassays are examined on the basis of a theoretical expression developed in the context of quantitative affinity chromatography [Nichol, L. W., Ward, L. D., and Winzor, D. J. (1981) Biochemistry 20, 4856–4860] but which is also pertinent to antigen-antibody interactions that may be described in terms of a single intrinsic association constant. Quantitative relationships are generated which provide the basis for more rigorous logit-log analyses of radioimmunoassays in which the antigen is multivalent, and an additional, theoretically superior, linear transform of the basic expression is developed. Simulated binding data for a tetravalent antigen system are then used to demonstrate (i) the curvilinearity of the conventional Scatchard plot for such a system despite the homogeneity of binding sites, and (ii) the application of the various linear transforms involving logarithmic functions. Of particular interest in that regard is the observation that the traditional logit-log analyses yield linear plots with the predicted slope of unity even though antigen univalence is an implicit assumption in their application. Results obtained in a solid-phase radioimmunoassay of triiodothyronine are then presented to provide, for that system at least, experimental justification of the above-mentioned assumption that the antibody-antigen interactions may be described in terms of a single intrinsic association constant. Finally, an enzyme-linked immunoassay of ferritin is used to illustrate the possibility that a linear Scatchard plot may be obtained with a multivalent antigen under conditions where steric factors restrict participation of an antigen molecule to a single interaction with immobilized antibody.

?-Adsorption analysis of a substance with allowance for effect of heavy impurities

?-Adsorption analysis of a substance with allowance for effect of heavy impurities

Application of functional analysis to oscillatory ship model testing

The need for data relating to fluid forces and moments has led to general acceptance of oscillatory testing of ship models. Although the technique is well established, certain problems still attend the interpretation of results. The nature of the difficulties is explained and they are elucidated by making allowance for time history effects, using functional analysis. Allowance for these effects in this way also establishes that certain results which have hitherto been assumed to require nonlinear representations are in fact capable of very accurate linear specification.

The influence of interactions between electrode processes on the structure of the equivalent electrical circuit for the electrode-solution interface

Summary It is shown in the case of a simple electrode reaction with nonlinear adsorption of the two reactants that there is no discrepancy between the electrical characteristics of the aperiodic circuit derived by intuitive reasoning and the corresponding symmetrical periodic circuit indicated by the impedance matrix theory approach of Grafov and Pekar. The representation in the aperiodic circuit of complications caused by parallel charge transfer reactions when a reactant is adsorbed in different forms, or at different sites, is considered. The thermodynamic significance of voltages appearing in aperiodic circuits is discussed and the modifications needed when allowance for effects due to component non-linearity or to changes in interfacial temperature or pressure must be made are briefly outlined.

Electrical resistivity of the earth's core

Allowance for effect of impurities in the iron of the earth's fluid core increases its electrical resistivity by a factor of about 10 over previous estimates, to a new preferred value 3 × 106 emu (3 × 10−5 ohm m). Extrapolations of the resistivity of pure liquid iron to probable temperatures and pressures of the core only involve factors of 1.6 and 1.3 and are slight compared with the impurity effect. The plausible range of values is 106 to 2 × 107 emu, which could be substantially narrowed by resistivity measurements on iron alloys in the liquid state. The new estimate strongly favours precessional torques rather than convection as the driving mechanism for the geomagnetic dynamo.

Absolute isotopic abundance ratios of three common lead reference samples

The absolute isotopic abundance ratios have been determined for three common lead reference samples, using solid-sample mass spectrometry. Samples of known isotopic composition, prepared from nearly pure separated 206Pb and 208Pb isotopes, were used to calibrate the mass spectrometers. The resulting absolute values are as follows: GS 4: 204Pb/206Pb = 0.061888 ± 0.000065, 207Pb/206Pb = 0.95342 ± 0.00036, 208Pb/206Pb = 2.2181 ± 0.0010; NBS 200: 204Pb/206Pb = 0.068353 ± 0.000072, 207Pb/206Pb = 1.00538 ± 0.00038, 208Pb/206Pb = 2.3675 ± 0.0011; C.I.T. Pb Std.: 204Pb/206Pb = 0.060151 ± 0.000063, 207Pb/206Pb = 0.93081 ± 0.00035, 208Pb/206Pb = 2.1835 ± 0.0010. The indicated uncertainties are overall limits of error based on 95% confidence limits for the mean and allowances for effects of known sources of possible systematic error.

Absolute Isotopic Abundance Ratios and Atomic Weight of Magnesium.

Absolute values have been obtained for the isotopic abundance ratios of magnesium, using surface emission mass spectrometry. Samples of known isotopic composition, prepared from nearly pure separated magnesium isotopes, were used to calibrate the mass spectrometers. The resulting absolute values are 25Mg/24Mg = 0.12663 ±0.00013 and 26Mg/24Mg = 0.13932 ± 0.00026, yielding an atomic weight (12C = 12) of 24.30497 ±0.00044. The indicated uncertainties are overall limits of error based on 95 percent confidence limits for the mean and allowances for effects of known sources of possible systematic error.

Absolute Isotopic Abundance Ratios and the Atomic Weight of a Reference Sample of Chromium.

Absolute values have been obtained for the isotopic abundance ratios of a reference sample of chromium, using surface emission mass spectrometry. Samples of known isotopic composition, prepared from nearly pure separated chromium isotopes, were used to calibrate the mass spectrometers. The resulting absolute values are Cr50/Cr52 = 0.051859 ±0.000100, Cr53/Cr52 = 0.113386 ±0.000145, Cr54/Cr52 = 0.028222 ±0.000059, yielding an atomic weight (CI2=12) of 51.99612 ±0.00033. The indicated uncertainties arc overall limits of error based on 95 percent confidence limits for the mean and allowances for effects of known sources of possible systematic error.

Natural variations in the abundance ratio and the atomic weight of copper

The absolute ratio Cu63/Cu65 was determined for 106 samples that include a variety of copper minerals. Relative to a reference copper sample with a previously determined absolute ratio of 2.2440±0.0021, variations range from −9.0 to +3.3‰ (1.5‰ = 95% confidence limit of a single determination). No significant variations were found for chalcopyrite, tetrahedrite, enargite, or in the Canyon Diablo and Bruderheim meteorites. Some samples of bornite and of chalcocite exhibit variations with enrichments in either Cu63 or in Cu65. Secondary oxides of copper show significant enrichment only in the heavy isotope. The relative variations previously reported by Walker, Cuttitta, and Senftle for samples from the Cougar mine, Colorado, are confirmed. A mean value of 2.2431 for 82 mineral samples probably is unduly weighted with the rarer secondary minerals that are enriched in Cu65. The ratio Cu63/Cu65 for bulk or commercially processed copper is very near the value of 2.2440, and the atomic weight of such copper is 63.5455±0.0010. The causes of the natural variations in copper abundance ratios are not known. Unless otherwise stated the indicated uncertainties are over-all limits of error based on 95% confidence limits for the mean and on allowances for effects of known sources of possible systematic error.

Absolute Isotopic Abundance Ratio and the Atomic Weight of Silver1a

An absolute value for the isotopic abundance ratio of natural silver was obtained by the use of isotopic standards prepared from nearly pure separated silver isotopes. Mass spectrometric data resulted in a value for the ratio (Ag/ sup 107//Ag/sup 109/ = l.0754/sub 7/ plus or minus 0.0013). Within the sta ted limits, no variation in natural abundance was found among six samples of native silver and commercial silver nitrate. A seventh native silver sample, obtained from Cobalt, Ontario, showed a statistically significant deviation. The calculated physical and chemical atomic weights of silver are respectively. On the recently proposed unified physcial and chemical atomic weight scale (C/sup 12/ = 12), the atomic weight is 107.8685 plus or minus 0.0013. The indicated uncertainties are overall limits of error based on 95% coafidence limits for the mean and on allowances for effects of known sources of possible systematic error. (auth)