An approximate molecular-orbital exchange theory is derived in which the various contributions to the exchange interaction are expressed explicitly as functions of the covalency amplitudes, overlaps, single-ion Coulomb and exchange integrals and charge-transfer excitation energies. The relative sizes of contributions of the same type to the different pairwise interactions between electrons occupying specific orbitals on neighboring sites can be evaluated fairly reliably from such a theory. Fixing over-all scale factors for the kinetic and potential exchange to produce agreement with ground-state exchange constants then has the effect of incorporating higher-order relaxation and correlation effects into the theory and making it relatively insensitive to some of the approximations which enter into its derivation. Application of the theory to the ground-state exchange constants of Mn${\mathrm{F}}_{2}$, KMn${\mathrm{F}}_{3}$, Ni${\mathrm{F}}_{2}$, and KNi${\mathrm{F}}_{3}$ not only determines the required scale factors, which prove to agree adequately with simple a priori estimates, but also produces interesting information on the relative sizes of different components of the covalent bonding: ${p}_{\ensuremath{\sigma}}$, ${p}_{\ensuremath{\pi}}$, and ${s}_{\ensuremath{\sigma}}$. Properties derived from the exchange interactions of the excited $^{4}E(I)$ multiplet in Mn${\mathrm{F}}_{2}$ are then deduced from the theory and compared to the experimental results. The agreement is fair to excellent for all quantities studied: two dispersion constants and two exciton-magnon coupling constants.

The optical absorption spectrum of Mn++ salts is typically dominated by spin-wave sidebands of forbidden ``atomic'' transitions. The Mn++ excited states are properly described as Frenkel excitons. Their dispersion, as well as their exchange interactions with the surrounding ions, arise from the same sort of ``super-exchange'' processes which determine the ground-state exchange constants. It would be useful to have a unifying descriptive framework for such interactions. In the study of a particular case, the 4E(I) excitons in MnF2, such a phenomenological theory has been constructed. Using the familiar MO description of the weak covalent bonding characteristic of these materials, the exchange interaction can be expressed in terms of a small number of parameters. These are determined from the ground-state exchange constants and then employed to predict properties of the excited states. The order-of-magnitude of the exciton dispersion is correctly given for both Eθ (−74 cm−1) and Eε (≈0 cm−1). The predicted interaction parameters which determine the binding energies of the Eθ exciton-magnon bound states are also qualitatively correct.

A careful discussion is given of the application of the resolvent or Koster-Slater method to a surface-state problem described by a model Hamiltonian of the tight-binding type. Because of a special symmetry, peculiar to the surface-state problem, it is possible to reduce the degree of the characteristic determinant by a factor of 2. The usual, "truncation" method of doing this is shown to sometimes lead to spurious solutions. The origin and properties of these are determined and a prescription for recognizing them presented. An alternative, "pre-severed" approach to the reduction of the determinant is described. This latter is less useful for numerical calculation, but has advantages in obtaining analytical results. The general form of the surface-state wave function is derived from the integral representation of the resolvent. It proves possible to characterize this form using only simple properties of the bulk band structure as represented by the model Hamiltonian. This then permits the popular "ansatz" method of treating the surface states to be routinely used in problems having an arbitrary degree of complexity. The results of the general discussion are applied to determine the surface states associated with the (110) cleavage face of a semiconductor having the zinc-blende structure. The "pre-severed" resolvent method is used to derive some preliminary analytical results, and a program is set up for the numerical calculation of the surface-state properties for more realistic models of the surface perturbation.

This paper discusses in detail the critical properties of a class of particularly simple ferrimagnets typified by simple cubic and body-centered cubic lattices having alternate sites occupied by classical spins of different magnitudes, ${S}_{A}$ and ${S}_{B}$. Heisenberg exchange interactions are assumed to act between nearest-neighbor sites. For such ferrimagnets, general arguments are presented which determine certain features of the dependence of the susceptibility $\ensuremath{\chi}$ and the specific heat on the variables $R=\frac{{S}_{B}}{{S}_{A}}$ and $j=\frac{{S}_{A}{S}_{B}J}{\ensuremath{\kappa}T}$. It is easily shown that the critical point occurs at a fixed $|j|$ for either sign of the exchange and arbitrary spin values. Moreover, the exponent $\ensuremath{\gamma}$ of the singularity in $\ensuremath{\chi}$ has a value independent of the sign of the exchange and of the spin values. The only exception permitted occurs at the singularity of the simple antiferromagnet ($R=1$, $j<0$) which has a reduced critical exponent. The nature of the dependence of $\ensuremath{\chi}$ on $R$ permits one to obtain its expansion in powers of $j$ from the known expansion coefficients for the related ferromagnet. A Pad\'e-approximant study of $\ensuremath{\chi}$ for a range of $R$ values is described. For $R\ensuremath{\ne}1$, the dominant singularity for positive and negative $j$ shows the familiar power-law behavior and is consistent with the general features of the $R$ dependence described above. The critical points and exponents are estimated for the cases studied by a new method making use of the freedom to vary $R$ in the ferrimagnet. A method of characterizing the weaker singularities in $\ensuremath{\chi}$ is described and investigated numerically. The implications of these results for real ferrimagnets are examined.

This paper deals with the critical properties of a class of particularly simple ferrimagnets. We consider the simple cubic and bcc lattices having alternate sites occupied by spins of different magnitudes, SA and SB. Classical Heisenberg exchange interactions are assumed to act between nearest-neighbor sites. For such ferrimagnets, general arguments determine certain features of the dependence of the susceptibility χ and the specific heat on the variables R = SA/SB and j = SASBJ/κT. We are able to show that the critical point occurs at a fixed | j | for either sign of the exchange and arbitrary spin values. Moreover, the exponent γ of the singularity in χ has a value independent of the sign of the exchange and of the spin values. The only exception permitted occurs at the singularity of the simple antiferromagnet (R = 1, j < 0), which has a reduced critical exponent. The nature of the dependence of χ on R permits one to obtain its expansion in powers of j from the known expansion coefficients for the related ferromagnet. A Padé approximant study of χ was carried out for a range of R values. For R ≠ 1, the dominant singularity for positive and negative j showed the familiar power law behavior and was consistent with the general features described above, The critical points and exponents were estimated for the cases studied by a new method making use of the freedom to vary R in the ferrimagnet.

The applicability of the Manley–Rowe relations is extended to the case of beams incident on a parallel-sided plate having rationally related frequencies but different angles of incidence. Distinct harmonic beams of the same frequency are distinguished by their different values of the transverse wave vector. The statement of the Manley–Rowe relations is changed only to the extent that terms corresponding to zero frequencies are omitted from the sums. This extension of the relations fills a gap which is inconvenient in discussions of the image-processing possibilities of nonlinear optical media.

1.A phosphoprotein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) was demonstrated in kidney. Phosphoprotein kinase activity was measured by determining the amount of 32P transferred from [γ-32P]ATP to 30–40% dephosphorylated Phosvitin.2.Methods of extracting phosphoprotein kinase from kidney were investigated. 0.05 M Na4P2O7 was found to be the best extractant.3.Intracellular distribution of phosphoprotein kinase activity was studied in hog, rat and rabbit kidneys. The major portion of the phosphoprotein-kinase activity was found in the kidney-supernatant fraction.4.Optimal conditions for the assay of kidney-phosphoprotein kinase activity were investigated. A bivalent metal ion was required and Mg2+ produced optimal activation. Co2+, Mn2+ and Ni2+ also activated kidney phosphoprotein kinase. With an optimal concentration of Mg2+ further activation was produced by potassium phosphate buffer, NaCl, KCl and Tris-HCl buffer. Phosvitin, 20–40% dephosphorylated by wheat-germ acid phosphatase (EC 3.1.3.2.), was the best substrate.5.The effect of inhibitors on kidney phosphoprotein kinase was studied. Iodoacetamide, N-ethylmaleimide and KF had no effect on enzyme activity. 2,4-Dinitrophenol inhibited kidney-phosphoprotein kinase. With an optimal concentration of Mg2+ the addition of other metal ions produced inhibition.6.A convenient method for the preparation and isolation of [γ-32P]ATP of high specific activity is described. The portion of the glycolytic pathway from fructose 1,6-diphosphate to 3-phosphoglyceric acid was used. The substrates and enzymes are avallable commercially.

The scattering of electrons by stacking faults is formulated for both h.c.p. and f.c.c. structures using orthogonalized-plane-waves and time dependent perturbation theory. For highenergy electrons (several times the Fermi energy) ordinary diffraction is obtained, with transition amplitudes first-order in the lattice potential. This scattering is not specular. At lower energies, corresponding to the Fermi energy in polyvalent metals, only electrons with large angles of incidence are diffracted to this order. Electrons with small angles of incidence are scattered only to higher order in the potential and only into the specularly reflected state. At still lower energies, corresponding to the Fermi energy in monovalent metals, all electrons are subject only to higher-order specular scattering.

Transhydrogenation from TPNH to DPN by an enzyme preparation from rat liver was mediated by 4.10−6M androsterone. The Δ4-3-oxosteroids inhibited this transhydrogenation at concentrations of 10−7 to 10−6M. The majority of the transhydrogenase inhibitors also inhibited DPN- and TPN-dependent dehydrogenation of androsterone. The inhibitory influence on hydrogen transfer was potentiated by the introduction of an additional double bond in ring A but depressed by substitution on position 17.

The plasma calcium was fractionated into protein-bound and free fractions by means of an ultracentrifuge in normal, hypoparathyroid and hyperparathyroid dogs and normal and hypoparathyroid rats. The proportion of the total plasma calcium that was diffusible was greater in normal and hypercalcemic animals than in the hypoparathyroid state. Recalcification of hypoparathyroid dog plasma in vitro gave a similar calcium distribution to that obtained when parathyroid extract was injected into hypoparathyroid dogs. Although the binding of calcium per gram of plasma protein increased both in vivo and in vitro as the concentration rose, the results did not conform to the simple mass law relationship as usually expressed. The evidence presented indicates that parathyroid function only influences the distribution of plasma calcium indirectly by regulating its concentration.

The method of obtaining protein-free calcium in plasma using the Spinco/ Beckman Model L Preparative Ultracentrifuge was investigated. It proved to be a simple procedure of high precision requiring the minimum of manipulation. The pH and temperature were easily and effectively controlled throughout the procedure. Equilibration with CO2 was eliminated. The protein-free calcium in 14 normal subjects was 53.5% of the total plasma calcium as compared with 60% in 3 cases of hyperparathyroidism.

A comparison has been made of the fate of C14-labeled corticosterone in intact, hepatectomized, bile fistula and ureteral ligated dogs. The rate of removal of activity from plasma is clearly reduced in the hepatectomized animal as compared to all other preparations. Radioautograms of plasma indicated that some change in corticosterone occurs soon after its injection regardless of whether or not the liver is present. In the dog both urine and feces are pathways of excretion for corticosterone and its metabolites. Evidence for an enterohepatic circulation of this steroid and its metabolites was obtained.

Nitrogen balance studies were conducted on 5 renal insufficient patients at several levels of protein intake. Similar observations were made on a healthy individual. The data indicate that renal insufficient patients manifesting slight to moderate azotemia had a higher than normal endogenous nitrogen metabolism and required a higher protein intake for nitrogen equilibrium than did the normal subject on the same diet. By means of retrogression curves, it was possible to predict the protein required for nitrogen equilibrium. The actual protein requirement for a given patient could not be predicted from any of the clinical measurements applied to these patients. Limited amino acid supplementation of the basic protein restricted diet failed to demonstrate any effect on the nitrogen requirement of these patients.

Abstract The distribution of fat in certain organs of rats and dogs was studied primarily by frozen sections stained with oil red O, at intervals from ten minutes to twenty-four hours after rapid intravenous administration of 0.6 to 1.2 Gm. per kilogram of olive oil in emulsified form. This was compared with the distribution of fat following similarly injected fatty dog chyle as well as that of olive oil administered by stomach tube. Olive oil in the amount of 2 ml. given by stomach tube to rats could not be identified in spleen, liver, or lungs. The fat of injected artificial emulsions always appeared by ten minutes after injection in large amounts in the marginal zone of the splenic red pulp. In contrast, the fat of dog chyle was never concentrated here. Within ten minutes after injection of chyle, fat appeared in the parenchymal cells of the liver of dogs; at this interval after artificial emulsion, fat was concentrated in the Kupffer cells. The evidence from rat livers was clouded by variable fat content in the livers of untreated rats. Kupffer cells of rats contained fat only in recently anesthetized animals which had received emulsion; there was some evidence that this fat was passed on to the parenchymal cells. Chyle fat was never concentrated in the Kupffer cells. Lung capillaries of rats were packed with fat ten minutes after injections of artificial emulsion, but at subsequent intervals only scattered droplets remained in the septal macrophages. Chyle fat was never concentrated in the lung. Fat did not appear in significant quantities outside the blood vessels in cervical lymph nodes, kidney, heart, thymus, stomach, duodenum, or ileum after injections of either chyle or emulsion. The sheathed arteries of the dog spleen were sites of a striking concentration of fat in dogs receiving either emulsion or chyle. No concentration of fat could be detected in the rat spleen that would correspond to sheathed arteries. Possible causes of the considerable variation in results are discussed and the need for a labeled fat for future experiments is indicated.

ArticleFree Plasma Levels and Urinary Excretion of Eighteen Amino Acids in Normal and Diabetic DogsJohn H. Ivy, Muriel Svec, and Smith FreemanJohn H. IvyFrom the Department of Experimental Medicine, Northwestern University Medical School, Chicago, Illinois, Muriel SvecFrom the Department of Experimental Medicine, Northwestern University Medical School, Chicago, Illinois, and Smith FreemanFrom the Department of Experimental Medicine, Northwestern University Medical School, Chicago, IllinoisPublished Online:30 Sep 1951https://doi.org/10.1152/ajplegacy.1951.167.1.182MoreSectionsPDF (1 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation More from this issue > Volume 167Issue 1September 1951Pages 182-192 Copyright & PermissionsCopyright © 1951 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1951.167.1.182PubMed14885486History Received 19 March 1951 Published online 30 September 1951 Published in print 30 September 1951 Metrics