Showing papers by "Iowa State University published in 1969"
TL;DR: In this paper, a simple method of assaying soil phosphatase activity is described, which involves colorimetric estimation of the p-nitrophenol released by the enzyme when the soil is incubated with buffered (pH 6·5) sodium pnphosphorus solution and toluene at 37°C for 1 hour.
Abstract: A simple method of assaying soil phosphatase activity is described. It involves colorimetric estimation of the p-nitrophenol released by phosphatase activity when soil is incubated with buffered (pH 6·5) sodium p-nitrophenyl phosphate solution and toluene at 37° C for 1 hr. The method is rapid and precise, and it has significant advantages over methods previously proposed for assay of soil phosphatase activity.
3,503 citations
TL;DR: In this paper, a non-linear regression calculation procedure was developed which permits calculation of surface tension and contact angle for any sessile drop shape with a contact angle greater than zero.
131 citations
TL;DR: The use of segments of polynomials to approximate production surfaces and time-series trends is described and illustrated in this paper, where segmented curves are restricted to be continuous and have a continuous derivative(s) at the join points.
Abstract: The use of segments of polynomials to approximate production surfaces and time-series trends is described and illustrated These segmented curves are restricted to be continuous and have a continuous derivative(s) at the join points
123 citations
114 citations
TL;DR: The authors discusses the case of inference for a simple experiment, the paired design, and proceeds to a comparison of three tests of significance which can be viewed as competitors in this design, i.e., the sign test, S, the Wilcoxon test, W, and the Fisher randomization test, R.
Abstract: For the past 40 years, there has been confusion on the differences between tests of significance and tests of hypotheses to the point where data interpretation is presented as an accept-reject process. This paper discusses the case of inference for a simple experiment, the paired design. It gives a rationale of the significance tester, and proceeds to a comparison of three tests of significance which can be viewed as competitors in the case of this design. These are the sign test, S, the Wilcoxon test, W, and the Fisher randomization test, R. The conclusion is that there is indeed an ordering of the tests, which is R preferred to W preferred to S. The S test should never be used if the others are possible. An Appendix gives a proof of monotonicity of the R test with respect to a shift alternative.
111 citations
TL;DR: The relative heat of formation and the reduced melting temperatures of the lanthanide compounds are correlated with the magnitude of the contraction in these compounds relative to the contraction of the pure metals.
Abstract: The relative heats of formation and the reduced melting temperatures (the melting point of the compound divided by the melting point of the metal) of the lanthanide compounds are correlated with the magnitude of the lanthanide contraction in these compounds relative to the lanthanide contraction in the pure metals If the lanthanide contraction (as determined from the lattice constants) in the compounds is greater than that observed for the metals, the heat of formation is expected to increase as one proceeds from lanthanum to lutetium The opposite is expected if the lanthanide contraction is less in the compounds than in the metals This has been substantiated for the five series for which sufficient thermodynamic data exist, specifically, RCd, RCl 3 , RH 2 , RMg and R 2 O 3 For the melting points, 15 of 17 lanthanide compound series show agreement between the observed reduced melting points and that expected from the relative lanthanide contraction Discrepancies are more likely to occur when correlating the melting points, since only part of the various bonds, RM, MM and RR, are broken upon melting, than for the heats of formation since this quantity is a measure of forming all of the bonds in the crystal
108 citations
TL;DR: In this paper, a detailed account of the calculation of the generalized susceptibility functions of Gd, Dy, Er, and Lu using realistic energy bands is given, and a fundamental understanding is obtained of the transition between the helical and the ferromagnetic state and of the anomalous thermal expansion in both ordered states.
Abstract: A detailed account is given of the calculation of the generalized susceptibility functions of Gd, Dy, Er, and Lu using realistic energy bands. These susceptibilities clearly show the influence of the Fermi-surface geometry in determining the helical ordering arrangements of the heavy rare earths, and the ferromagnetic ordering of Gd. A microscopic discussion of the magneto-elastic effect for a general ordered spin state is also presented. The first-order transition from the helical state to the ferromagnetic or conical ferromagnetic state in Tb, Dy, Ho, and Er is explained by this effect. Dy is used as an example of the application of the formalism, and a fundamental understanding is obtained of the transition between the helical and the ferromagnetic state and of the anomalous thermal expansion in both ordered states.
108 citations
TL;DR: In this paper, the relationship between the location of the non-lanthanide element partner in the Periodic Table and the valence state of europium and ytterbium in the various compounds is discussed.
Abstract: Europium and ytterbium are the only lanthanide metals which are divalent in their standard state. In some of their compounds these two metals are trivalent, e.g., the sesquioxides and trihalides. In order to form compounds in which europium and ytterbium are trivalent, the extra 4ƒ electron in the pure metals must be promoted to a valence or outer electronic level. The energy of promotion is calculated to be 23 and 9 kcal/g at. Eu and Yb, respectively. It is this energy of promotion which plays a decisive role in determining the valence state assumed by europium and ytterbium in their compounds. From the magnitudes of these values it is seen why there are more compounds in which ytterbium is trivalent than europium. The relationship between the location of the non-lanthanide element partner in the Periodic Table and the valence state of europium and ytterbium in the various compounds is discussed.
106 citations
TL;DR: In this paper, it is argued that to treat the quantum-mechanical effects appearing at large wave vectors properly, the nonlocal dielectric functions which appear in the expressions for the surface impedance should be finite-electron-lifetime generalizations of the Lindhard dielectrics rather than those resulting from the Boltzmann equation.
Abstract: Our previous studies of the optical properties of an electron gas for which the surface scattering is specular have been extended. It is argued that to treat the quantum-mechanical effects appearing at large wave vectors properly, the nonlocal dielectric functions which appear in the expressions for the surface impedance should be finite-electron-lifetime generalizations of the Lindhard dielectric functions rather than those resulting from the Boltzmann equation. The striking anomalous absorption, due to plasmon excitation, occurring above the plasma frequency is emphasized in the discussion of the semi-infinite gas. For the case of a slab, the thickness dependence of the processes characterizing the optical properties is discussed. Electron-gas parameters representing both K and Al were used in the calculations, as were both types of dielectric functions mentioned above. A comparison of the present theory with some alternative theories, particularly that of Melnyk and Harrison, is presented.
102 citations
98 citations
TL;DR: The kinetic mechanism of action of adenylosuccinate synthetase from Escherichia coli, strain B, was investigated from initial rate studies and a rapid equilibrium, fully random mechanism was found to be in harmony with the kinetic findings from studies with competitive and product inhibitors.
TL;DR: In this paper, the finite-electron-lifetime expressions for the longitudinal and transverse dielectric functions of a freeelectron gas obtained by Lindhard in the self-consistent field approximation are examined.
Abstract: The finite-electron-lifetime expressions for the longitudinal and transverse dielectric functions of a free-electron gas obtained by Lindhard in the self-consistent-field approximation are examined. It is shown that these results are incorrect, and appropriate expressions are developed for the case where the system can be characterized by a single relaxation time.
TL;DR: The Young's, shear, and bulk moduli of polycrystalline TiB2, ZrB2 and HfB2 were determined from 298 ° to 1300 °K by the sonic resonance technique as mentioned in this paper.
Abstract: The Young's, shear, and bulk moduli of polycrystalline TiB2, ZrB2, and HfB2 were determined from 298 ° to 1300 °K by the sonic resonance technique. All three of these moduli decreased by about 9% over the temperature range considered. The Young's and shear moduli were fitted to Wachtman's empirical equation. The theoretical Soga-Anderson equation was applied to the bulk modulus-temperature data and found to fit the data within 1% despite the variation of the Soga-Anderson constant, δ, with temperature. The Gruneisen constant, γ, was found to remain invariant with temperature while the Poisson's ratio increased with increasing temperature. Debye temperatures were computed from the measured Young's and shear moduli.
TL;DR: In this article, the CD spectra of a number of rigid aromatic compounds containing an asymmetric center adjacent to the aromatic ring are reported, and a quadrant rule is proposed to predict the absolute configuration of molecules possessing an asymptotic center.
TL;DR: In this article, a theory assuming specular scattering of electrons and incorporating nonlocal transverse and longitudinal dielectric functions predicts that a thin metallic film may exhibit anomalous optical properties due to the wave-vector-dependent structure in the longitudinal Dielectric function.
Abstract: A theory assuming specular scattering of electrons and incorporating nonlocal transverse and longitudinal dielectric functions predicts that a thin metallic film may exhibit anomalous optical properties due to the wave-vector-dependent structure in the longitudinal dielectric function.
TL;DR: In this paper, the authors used 15N-enriched nitrite and found that soil pH and organic matter content are the key factors in nitrite decomposition and fixation of nitrite N in soils.
Abstract: Tracer studies using 15N-enriched nitrite showed that soil pH and organic matter content are the key factors in nitrite decomposition and fixation of nitrite N in soils. The extent of nitrite decomposition and fixation of nitrite N was inversely related to soil pH. With soils having pH values between 5 and 7, the amount of nitrite N fixed and the amount volatilized at a given pH increased with increase in soil organic matter content; with soils having pH values less than 5, the amount of nitrite N fixed increased, and the amount of nitrite N volatilized decreased, with increase in soil organic matter content. Air-drying of soils treated with nitrite promoted nitrite decomposition, but did not markedly affect fixation of nitrite nitrogen. The amount of nitrite decomposed and the amount of nitrite N fixed on incubation of soils treated with nitrite increased with increase in nitrite level and in time and temperature of incubation. Increase in soil moisture content above a certain level decreased the amount of nitrite N volatilized during incubation of nitrite-treated soils, but did not markedly affect the amount of nitrite N fixed. Sterilization of soil before treatment with nitrite had little effect on nitrite decomposition or fixation of nitrite nitrogen. Nitrite decomposition and fixation of nitrite N occurred readily under conditions commonly encountered in the field.
TL;DR: The most potent inhibitor of the brain hexokinase appears to be ADP, and all allosteric effectors were found to be inhibitory.
TL;DR: In this paper, the image force method is used to analyze the changes in the stress field of a screw dislocation caused by differences in the shear moduli on either side of a boundary and within the boundary.
TL;DR: The half-lives of several short-lived isotopes of Kr, Rb, Sr, Xe, Cs and Ba have been measured using sources of isotopically pure Xe or Kr and multi-scaling selected transitions in the Ge(Li) gamma-ray spectra of their decays as mentioned in this paper.
TL;DR: The Young's and shear moduli of polycrystalline yttrium oxide, dysprosium oxide, holmium oxide and erbium oxide were determined at room temperature as a function of volume fraction porosity using the sonic resonance technique as mentioned in this paper.
Abstract: The Young's and shear moduli of polycrystalline yttrium oxide, dysprosium oxide, holmium oxide, and erbium oxide were determined at room temperature as a function of volume fraction porosity using the sonic resonance technique. Linear relations empirically described the data for Y2O3, Hr2O3, and Er2O3. The Young's and shear moduli data for Dy2O3 were empirically described by Hasselman's and Spriggs’equations, respectively. The empirical curves which best fit the data were compared to theoretical expressions and agreed closely with a modified form of Mackenzie's equation. Values for bulk modulus, Poisson's ratio, and the Debye temperature were computed for each oxide, and the bulk modulus-volume relation was determined and compared to that of other oxides.
TL;DR: The thermal conductivities of gadolinium, terbium, and holmium single crystals have been measured as a function of temperature from 5 to 300\ifmmode^\circ\else\textdegree\fi{}K.
Abstract: The thermal conductivities of gadolinium, terbium, and holmium single crystals have been measured as a function of temperature from 5 to 300\ifmmode^\circ\else\textdegree\fi{}K. The steady-state heat-flow method was used. For each element measurements were taken in the $〈11\overline{2}0〉$ ($a$-axis) and in the $〈0001〉$ ($c$-axis) directions of the hexagonal close-packed crystal structure. Electrical resistivity measurements were made on the same samples to obtain Lorenz functions. Anomalies near magnetic transition temperatures are interpreted in terms of magnetic superzones and spin-disorder scattering. High-temperature anisotropy is interpreted in terms of Fermi-surface anisotropy. Lorenz numbers appreciably larger than ${L}_{0}$ suggest that phonons and magnons, in addition to electrons, can carry heat.
TL;DR: In this article, compressive deformation behavior of polycrystalline iron-aluminum alloys has been investigated at 298°K for specimens heat treated in various ways and containing from 22.0 to 31.7 at% Al.
Abstract: The compressive deformation behavior of polycrystalline iron-aluminum alloys has been investigated (i) at 298°K for specimens heat treated in various ways and containing from 22.0 to 31.7 at% Al, and (ii) from 77 to 655°K for well-annealed specimens containing 26.6 at% Al. Alloys which possess significant DO3 type long range order exhibit marked composition and temperature dependent variations in deformation behavior. Specifically, those containing ⪆ 27 at% Al exhibit two linear and one parabolic deformation stage at 298°K. The linear stages are shown to be a result of the production and motion of DO3 type superlattice dislocations. The absence of these stages in well-annealed specimens is attributed to the lack of thermal assistance for the DO3 superlattice dislocation nucleation process. The flow stress levels which characterize the two linear stage behavior agree with calculations of the stress required for production of antiphase boundaries. Results obtained from quenched specimens are in agreement with the above conclusions, and the changes induced by quenching are in accord with calculations of the effect of thermal antiphase boundaries upon dislocation motion.
Das Verformungsverhalten bei Kompression von polykristallinen Eisen-Aluminium-Legierungen wurde: 1. bei 298°K fur Proben, die in verschiedener Weise getempert waren und zwischen 22,0 und 31,7 At% Al enthielten und 2. zwischen 77 und 655 °K fur ausgetemperte Proben mit 26,6 At% Al untersucht. Legierungen, die eine betrachtliche Fernordnung von DO3-Typ besitzen, zeigen merkliche Anderungen im Deformationsverhalten, die von Zusammensetzung und Temperatur abhangen. Proben mit ⪆ 27 At% Al zeigen spezifisch einen parabolischen und zwei lineare Deformationsstufen bei 298 °K. Es wird gezeigt, das die linearen Stufen ein Ergebnis der Bildung und Wanderung von Versetzungen des DO3-Ubergitters sind. Das Fehlen dieser Stufen in ausgetemperten Proben wird dem Fehlen thermischer Assistenz fur den Bildungsprozes der DO3-Ubergitterversetzungen zugeschrieben. Die niedrigen Flusniveaus, die das Verhalten der beiden linearen Stufen charakterisieren, stimmen mit den Berechungen der Spannungen uberein, die fur die Bildung von Antiphasengrenzen notwendig sind. Die Ergebnisse, die fur die getemperten Proben erhalten werden, befinden sich in Ubereinstimmung mit den oben angefuhrten Schlussen, und die durch Tempern induzierten Anderungen stimmen mit Berechnungen des Einflusses der thermischen Antiphasengrenzen auf die Versetzungswanderung uberein.
TL;DR: In this article, an antisymmetrized product of interacting geminals is proposed for the form of a manyelectron wave function, where the interacting gems are given a natural orbital expansion where the natural orbits of the geminals are also natural orbitals of the total wave function.
Abstract: An antisymmetrized product of “interacting” geminals is proposed for the form of a many‐electron wavefunction. The interacting geminals are given a natural orbital expansion where the natural orbitals of the geminals are also natural orbitals of the total wavefunction. This ansatz is more general than the strongly and weakly orthogonal geminal and identical geminal models and includes them as particular cases. However, the use of the interacting geminal wavefunction is not significantly more complicated for the purpose of calculations. Different constraints on the geminal occupation coefficients define the various geminal models and more than one model can be incorporated into a single wavefunction. The case of two singlet pairs of electrons is examined in terms of the interacting geminal model—density matrices, energy expressions, and variational equations being given.
TL;DR: Neither starvation for 8 days nor feeding with a concentrate diet for at least 3 months before slaughter produced enzyme patterns in the tissues different from those in cattle given only hay, except that the all-concentrate diet caused increased activities of glucose 6-phosphate dehydrogenase and ;malic enzyme' in adipose tissues.
Abstract: The activities of phosphoenolpyruvate carboxykinase, ;malic enzyme', citrate-cleavage enzyme and glucose 6-phosphate dehydrogenase were assayed in homogenates of rumen mucosa, liver and adipose tissue of cattle. Rumen mucosa cytoplasm contained activities of ;malic enzyme' approximately sevenfold those of phosphoenolpyruvate carboxykinase, suggesting that the conversion of propionate into lactate by rumen mucosa involves ;malic enzyme'. Neither starvation for 8 days nor feeding with a concentrate diet for at least 3 months before slaughter produced enzyme patterns in the tissues different from those in cattle given only hay, except that the all-concentrate diet caused increased activities of glucose 6-phosphate dehydrogenase and ;malic enzyme' in adipose tissues. Rumen mucosa, liver and adipose tissue contained phosphoenolpyruvate carboxykinase activity. ;Malic enzyme' was absent in liver. Citrate-cleavage enzyme activity was present in liver and adipose tissue but was quite low in rumen mucosa. Liver contained much less glucose 6-phosphate dehydrogenase activity than rumen mucosa or adipose tissue.
TL;DR: The experiment described in this letter was undertaken to establish the specificity of porcine pancreatic amylase acting on “stubbed” starch oligosaccharides, to which single glucose units (stubs) are linked by a-1, 6-bonds.
TL;DR: Examination of urinary metabolites of 32 P- and 35 S-parathion orally administered to rats confirmed that initial metabolism of parathion involved activation to paraoxon and degradation to diethyl phosphorothioic acid.
TL;DR: In this paper, the relationship of stability constants to parameters such as the size of ions and the dielectric constant of solvents is clarified, and the relationship between stability constants and other parameters is discussed.
Abstract: It is the purpose of this paper to clarify the relationship of equations relating stability constants to parameters such as the size of ions and the dielectric constant of solvents to one another a...
TL;DR: In this paper a theory is developed which concerns itself with the stability of discrete systems over a finite interval of time and is general enough so as to include unforced systems, systems under the influence of perturbing forces, linear systems, non-linear systems, time invariant Systems, time-varying systems, simple systems and composite systems.
Abstract: In many cases of practical interest there is concern with the behaviour of dynamic systems only over a finite time interval. This concern may arise in one of two ways: In one case the system under consideration is defined over a fixed and finite interval of time, while in the second case the system in question is defined for all time; however, the behaviour of the system is of interest only over a finite time interval. Recently, Weiss and Infante (1965, 1967) treated the problem of system stability over a finite time interval for the ease of continuous systems. In this paper a theory is developed which concerns itself with the stability of discrete systems over a finite interval of time. The dynamic systems which are considered are general enough so as to include unforced systems, systems under the influence of perturbing forces, linear systems, non-linear systems, time invariant systems, time-varying systems, simple systems and composite systems. In the present development various definitions of stabilit...