The possibility of magnetic-order induced phonon anisotropy in single crystals of MnO and NiO is investigated using inelastic neutron scattering. Below TN both compounds exhibit a splitting in their transverse optical phonon spectra of approximately 10%. This behavior illustrates that, contrary to general assumption, the dynamic properties of MnO and NiO are substantially non-cubic.PACS numbers: 75.30.Gw, 78.70.Nx The failure of ab initio approximations to correctly incorporate many-body effects such as electron exchange and correlation is an issue at the core of contemporary solid-state research. Although these effects are important in almost all solids, they are essential for a proper description of co-operative phenomena such as antiferromagnetism, charge-ordering, superconductivity and colossal magnetoresistance.Despite the status of MnO and NiO as benchmark materials for the study of correlated electron systems and frequent use in first principles electronic structure investigations, many aspects of the physics of the 3d transition metal monoxides requires better theoretical explanation. For example, the basic physical properties predicted for MnO and NiO (e.g. band-gaps, distortion angles and phonon spectra) differ radically depending upon which techniques have been employed [1,2].In a recent publication comparing different ab initio and model band-structure models on MnO (including local spin-density approximation (LSDA) and 'LSDA + model' calculations), Massidda et al. [2] suggest that although the electronic density in MnO is approximately cubic, the lowering of symmetry associated with antiferromagnetic ordering can induce an electronic response that is significantly non-cubic. This results in the dynamical properties of the system, such as transverse optical (TO) phonons, exhibiting substantial "magneticorder induced anisotropy".One of the predicted features from such calculations is that the zone center (ZC) optical phonon modes should split depending on their polarization. A higher energy occurs for a mode polarized along the [111] direction and a lower energy for degenerate modes polarized in the orthogonal ferromagnetic plane, see Table I. Massidda et al. [2] find that this effect arises solely due to the magnetic ordering, and would even occur in the absence of any rhombohedral distortion. By comparing results from four different approximation schemes, lower and upper bounds of 3-10% for the magnitude of the splitting are estimated. Variations in the splitting due to the distortion are calculated to be less than 1%.Although similar theoretical calculations have not yet been performed for NiO, the results of measurements of NiO TO phonons are predicted to be qualitatively similar to those in MnO. Indeed, it has been suggested that the splitting in NiO may be even greater in absolute magnitude than in MnO due to the larger magnetic superexchange [3].MnO and NiO are classic examples of type-II antiferromagnets possessing the cubic rock-salt structure. Below T N , exchange-striction causes contra...
Since the establishment of the 1998 folate recommended dietary allowance (RDA), the methylenetetrahydrofolate reductase (MTHFR) 677C-->T variant has emerged as a strong modifier of folate status. This controlled feeding study investigated the adequacy of the RDA, 400 microg/d as dietary folate equivalents (DFE), for Mexican American men with the MTHFR 677CC or TT genotype. Because of the interdependency between folate and choline, the influence of choline intake on folate status was also assessed. Mexican American men (n = 60; 18-55 y) with the MTHFR 677CC (n = 31) or TT (n = 29) genotype consumed 438 microg DFE/d and total choline intakes of 300, 550 (choline adequate intake), 1100, or 2200 mg/d for 12 wk. Folate status response was assessed via serum folate (SF), RBC folate, plasma total homocysteine (tHcy), and urinary folate. SF decreased (P < 0.001) 66% to 7.9 +/- 0.7 nmol/L (means +/- SEM) in men with the 677TT genotype and 62% to 11.3 +/- 0.9 nmol/L in the 677CC genotype. Plasma tHcy increased (P < 0.0001) 170% to 31 +/- 3 micromol/L in men with the 677TT genotype and 18% to 11.6 +/- 0.3 micromol/L in the 677CC genotype. At the end of the study, 34% (677TT) and 16% (677CC) had SF concentrations <6.8 nmol/L and 79% (677TT) and 7% (677CC) had tHcy concentrations >14 micromol/L. Choline intake did not influence the response of the measured variables. These data showed that the folate RDA is not adequate for men of Mexican descent, particularly for those with the MTHFR 677TT genotype, and demonstrated a lack of influence of choline intake on the folate status variables measured in this study.
Let M be a countably infinite ω-categorical structure. Consider Aut(M) as a complete metric space by defining d(g, h) = Ω{2−n: g (xn) ≠ h(xn) or g−1 (xn) ≠ h−1 (xn)} where {xn : n ∈ ω} is an enumeration of M An automorphism α ∈ Aut(M) is generic if its conjugacy class is comeagre. J. Truss has shown in [11] that if the set P of all finite partial isomorphisms contains a co-final subset P1 closed under conjugacy and having the amalgamation property and the joint embedding property then there is a generic automorphism. In the present paper we give a weaker condition of this kind which is equivalent to the existence of generic automorphisms. Really we give more: a characterization of the existence of generic expansions (defined in an appropriate way) of an ω-categorical structure. We also show that Truss' condition guarantees the existence of a countable structure consisting of automorphisms of M which can be considered as an atomic model of some theory naturally associated to M. We do it in a general context of weak models for second-order quantifiers.The author thanks Ludomir Newelski for pointing out a mistake in the first version of Theorem 1.2 and for interesting discussions. Also, the author is grateful to the referee for very helpful remarks.
Choline is a required nutrient with roles in liver and brain function, lipid metabolism, and fetal development. Recent data suggest that choline requirements may be altered by polymorphisms in the phosphatidylethanolamine N-methyltransferase (PEMT) gene (i.e., 5465G→A; rs7946 and -744G→C; rs12325817) and in the methylenetetrahydrofolate dehydrogenase (MTHFD1) gene (i.e., 1958G→A; rs2236225). This controlled feeding study, conducted in 2000-2001, examined the effects of the PEMT and MTHFD1 genetic variants on biomarkers of choline metabolism in premenopausal Mexican American women (n=43) after a 7-wk period of folate restriction (135μg as dietary folate equivalents, DFE) and after a 7-wk period of folate treatment (400 and 800μg DFE/d combined). Throughout the 14-wk study choline intake remained constant at 349mg/d. The genotype frequencies of the women were 3GG, 19GA, and 21AA for PEMT G5465A; 9GG, 17GC and 17CC for PEMT G-744C; and 9GG, 21GA and 13AA for MTHFD1 G1958A. During folate restriction, homocysteine was adversely influenced by PEMT 5465AA (P=0.001 relative to the G allele) and by MTHFD1 1958AA (P=0.085 relative to 1958GG); whereas the decline in phosphatidylcholine was attenuated by PEMT -744CC (P=0.017 relative to -744GG). During folate treatment, no effects of the genotypes on the response of the measured variables were detected. These data suggest that polymorphisms in genes relevant to choline metabolism modulate parameters of choline status when folate intake is restricted. Additional studies with larger samples sizes are needed to examine the relationship between these genetic variants and varied choline intake in populations with increased demands for choline (i.e., pregnant women).
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