Heisenberg spin chains: Quantumclassical crossover and the Haldane conjecture J. Appl. Phys. 57, 3319 (1985); 10.1063/1.335134
Field dependent neutron scattering study of the quasi 2D Heisenberg antiferromagnet K2MnF4Our studies of the spin dynamics for two near-Heisenberg antiferromagnets (AFMs) revealed:In CsNiC1 3 (S = 1) at low T < TN we confirm the conclusions given earlier, but disagreement with the spin-wave calculations used is found for the eigenvectors. For T> 1'. .. , the most important result is the observation that ali (sa sa) (a = x,y,z) are identical, demanding another interpretation for the gap observed than the easy axis one. In CsVC1 3 (S =~) we could not observe any inconsistency in the microscopic parameters determined above and below TN' Although there is a striking coincidence with Haldane's conjecture [unexplained gap for S = 1 (CsNiCI 3 ), no such gap for S = ~ (CsVC1 3 )], it is not clear whether this can be considered a prooffor Haldane's conjecture.
Diffraction intensity analysis of small-angle neutron scattering measurements of dry SBA-15 have been combined with nonlocal density functional theory (NLDFT) analysis of nitrogen desorption isotherms to characterize the micropore, secondary mesopore, and primary mesopore structure. The radial dependence of the scattering length density, which is sensitive to isolated surface hydroxyls, can only be modeled if the NLDFT pore size distribution is distributed relatively uniformly throughout the silica framework, not localized in a “corona” around the primary mesopores. Contrast matching-small angle neutron scattering (CM-SANS) measurements, using water, decane, tributylamine, cyclohexane, and isooctane as direct probes of the size of micropores indicate that the smallest pores in SBA-15 have diameter between 5.7 and 6.2 Å. Correlation of the minimum pore size with the onset of the micropore size distribution provides direct evidence that the shape of the smallest micropores is cylinderlike, which is consistent with their being due to unraveling of the polymer template.
Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) techniques have been applied to study the self-assembly processes of a microbially produced siderophore, marinobactin E (ME). ME is one of a series of marinobactins A-E that facilitate Fe(III) acquisition by the source bacterium through coordination of Fe(III) by the marinobactin headgroup. ME is a six-amino-acid peptide amphiphile appended by palmitic acid (C16), and differs only in the nature of the fatty acid moiety from the other marinobactins. Apo-ME (uncoordinated ME) assembles to form micelles with an average diameter of 4.0 nm. Upon coordination of one equivalent of Fe(III), the mean micellar diameter of Fe(III)-ME shrinks to approximately 2.8 nm. However, in the presence of excess Fe(III), Fe(III)-ME undergoes a micelle-to-vesicle transition (MVT). At a small excess of Fe(III) over Fe(III)-ME (i.e., <1.2 Fe(III)/ME), a fraction of the Fe(III)-ME micelles rearrange into approximately 200 nm diameter unilamellar vesicles. At even greater Fe(III)/ME ratios (e.g., 2-3) multilamellar aggregates begin to emerge, consistent with either multilamellar vesicles or lamellar stacks. The MVT exhibited by ME may represent a unique mechanism by which marine bacteria may detect and sequester iron required for growth.
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