Evidence for the surface origin of point defects in ice: control of interior proton activity by adsorbates

Spectroscopic studies are presented of H-D isotopic exchange in the interior of ice nanocrystals. The exchange process is dominated by ionic and orientational defects long viewed as governing the electrical properties of ice. A new finding that interior exchange rates can be controlled by acidic and basic adsorbates is evidence that the defects originate at the ice surface. In particular, it is argued that interior isotopic exchange is a reflection of proton concentrations equilibrated at the ice surface.     

Determination of the absolute configurations of natural products via density functional theory calculations of vibrational circular dichroism, electronic circular dichroism and optical rotation: the schizozygane alkaloid schizozygine

The development of density functional theory (DFT) methods for the calculation of vibrational circular dichroism (VCD), electronic circular dichroism (ECD), and transparent spectral region optical rotation (OR) has revolutionized the determination of the absolute configurations (ACs) of chiral molecules using these chiroptical properties. We report the first concerted application of DFT calculations of VCD, ECD, and OR to the determination of the AC of a natural product whose AC was previously undetermined. The natural product is the alkaloid schizozygine, isolated from Schizozygia caffaeoides. Comparison of DFT calculations of the VCD, ECD, and OR of schizozygine to experimental data leads, for each chiroptical technique, to the AC 2R,7S,20S,21S for the naturally occurring (+)-schizozygine. Three other alkaloids, schizogaline, schizogamine, and 6,7-dehydro-19beta-hydroxyschizozygine, have also been isolated from S. caffaeoides and shown to have structures closely related to schizozygine. Assuming a common biosynthetic pathway, their ACs are defined by that of schizozygine.     

Study of structural and electronic transport properties of Ce-doped LaMnO3

The structural and electronic transport properties of La_1−x Ce _x MnO₃ (x=0.0–1.0) have been studied. All the samples exhibit orthorhombic crystal symmetry and the unit cell volume decreases with Ce doping. They also make a metal-insulator transition (MIT) and transition temperature increases with increase in Ce concentration up to 50% doping. The system La_0.5Ce_0.5MnO₃ also exhibits MIT instead of charge-ordered state as observed in the hole doped systems of the same composition.     

A note on a problem of Erdös and Hajnal

In [5], Erdös and Hajnal formulate the following proposition, which we shall refer to as Φ: If ? is an order-type such that $\text{|?| = ω}{}_2\text{but}\text{ω}{}_2\text{, ω}{}_2{}^1\text{? ?}$, there is ψ ? ?, |ψ| = ω₁, such that $\text{ω}{}_1\text{, ω}{}_1{}^1\text{? ψ}$. In [2], we showed that if V = L, then ?Φ. We do not know if the assumption V = L can be weakened to CH, or if, in fact, Φ is consistent with CH. However, in this note we show that, relative to a certain large cardinal assumption, Φ is consistent with 2^ω = ω₂, so that ?Φ is not provable in ZFC alone. Our proof has an interesting model-theoretic consequence, which we mention at the end.     

Electronic transport and magnetic properties of the perovskites La0.8Sr0.2Co1−xFexO3; x ≤ 0.3

Transport and magnetic properties of LaCoO₃-based compounds, doped with 20% Sr and 2.5, 5, 10, 15, 20 and 30% Fe, were investigated by means of magnetization, resistivity and magnetoresistance measurements as well as by ⁵⁷Fe Mössbauer spectroscopy. While the temperature dependence of the dc and ac magnetic susceptibilities reveals the presence of magnetic phase separation accompanied by spin-glass and cluster-glass behavior, the electrical resistivity and magnetoresistance characteristics indicate that the mesoscopic structure of the present compounds is rather well described as consisting of ferromagnetic, metallic grains embedded in an insulating matrix. The effect of the partial Co → Fe substitution on the bulk magnetic and transport properties, as well as on the local state of Co and Fe ions is discussed.     

Prompt alpha decay of a well-deformed band in (58)Ni

Two excited well-deformed bands have been observed in the semi-magic nucleus (58)Ni. One of the bands was observed to partially decay by emission of a prompt discrete alpha particle that feeds the 2949 keV 6(+) spherical yrast state in the daughter nucleus (54)Fe. This constitutes the first observation of prompt alpha emission from states lying in the deformed secondary minimum of the nuclear potential. gamma-ray linking transitions via several parallel paths establish the spin, parity, and excitation energy of this deformed band in (58)Ni.     

Monte Carlo simulation for the formation of a mixed crystal from two solids in contact

The study focuses on nucleation and growth of a binary mixed crystal phase from two pure crystals in contact. Monte Carlo simulations of this process are conducted, with the dynamics proceeding via activated atom-vacancy exchanges. Intermolecular interactions, ranging up to next-nearest neighbors, are of size typical of hydrogen bonded systems. The process is driven by the formation of strong AB bonds at the expense of weaker AA and BB bonds. In the resulting model, the material is channeled and transported through the mixed phase crust along antiphase boundaries. The flow of molecules through the channels is directed, due to molecular energy lowering via gradual acquisition of an increasing number of nearest neighbors of the second species. On the other hand, defect motion is quasirandom. The model accounts partially for the t(1/alpha) (alpha>3) time dependence observed for conversion of nanoparticles of HBr dihydrate to monohydrate, by exposure to acid adsorbate.