Methyl 5-Bromolevulinate
Methyl 5-bromolevulinate (30%) is obtained directly by brominating levulinic acid in methanol. The synthesis of 5-aminolevulinic acid over the 5-phthalimido ester thus becomes a three-step one.
Materials Literature
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Standardization of convention for zero field splitting parameters
Transformation formulas have been derived for conversions between the various conventional systems for reporting zero field splitting data using the Hamiltonian H = D [Sz2 − (1/3)S(S + 1)] + E(Sx2−Sy2). It is recommended that all future work be reported in the standard system corresponding to the range −1≤3E/D≤0.
Electronic transport in ReO3: dc conductivity and Hall effect
The dc resistivity and low-field Hall effect of the transition-metal oxide Re${\mathrm{O}}_{3}$ have been measured as a function of temperature. The samples used were oriented single crystals which were large enough for measurements to be made by a conventional four-point probe method. The samples of Re${\mathrm{O}}_{…
Europium in the ultraphosphate lattice: Polarized spectra and structure of EuP5O14
The polarized emission and absorption spectra of single crystals of europium ultra(penta)phosphate, EuP5O14, were measured and interpreted. Most of the observed transitions were identified and the energy level structure of the 7F multiplet defined. The over-all site symmetry is found to be extremely low (C1), but in t…
Depolarized Rayleigh scattering in liquids. Molecular reorientation and orientation pair correlations in a nematic liquid crystal: MBBA
The spectrum and intensity of depolarized light scattered from binary solutions of the nematic MBBA and carbon tetrachloride have been measured. The results are interpreted in terms of pair correlations in the orientation of MBBA molecules. A systematic approach to the study of the orientational structure in nematic l…
Cooperative Jahn-Teller phase transition in PrAlO3
The perovskite PrAl${\mathrm{O}}_{3}$ is known to exhibit an apparently complicated series of structural phase transitions from cubic to rhombohedral orthorhombic to monoclinic and ultimately tetragonal symmetry at temperatures of 1320, 205, and 151 K, respectively. The 1320-K cubic-rhombohedral transition is a simple…
Thermoelectric power of the narrow-band Hubbard chain at arbitrary electron density: Atomic limit
We study the thermoelectric power of a narrow-band Hubbard chain with an arbitrary number of electrons per site. The calculations are carried out to the lowest order in the transfer integral. We find a characteristic electron density ($\ensuremath{\rho}=\frac{2}{3}$) below which the thermoelectric power is negative at…
Huang diffuse scattering from dislocation loops and cobalt precipitates in copper
High-resolution measurements of the Huang diffuse scattering from dislocation loops in neutron-irradiated copper and cobalt precipitates in Cu:1-wt%-Co crystals have been carried out close to the (200) and (111) reflections using a three-axis x-ray diffractometer. These measurements have been compiled in the form of d…
Strongly quenched deformation potentials of the Mn acceptor in GaAs
We have measured the luminescence spectrum of Mn-doped GaAs at liquid-He temperatures with and without an applied uniaxial stress. At zero stress we found clearly resolved donor-acceptor (DA) and band-acceptor recombination bands involving Mn. From these measurements we get a precise acceptor binding energy of 113 \if…
Effect of Molecular Weight on Glass Transition by Differential Scanning Calorimetry
The influence of molecular weight (900 to 1.8 × 10 6 ) on the glass transition temperature of low polydispersity polystyrene (anionically prepared) has been studied by differential scanning calorimetry at heating rates of 5 to 80 °C min −1 . Over the range of molecular_weight studied, and at an extrapolated heating ra…
On the growth-sectorial dependence of defects in natural diamonds
Abstract Certain rare diamonds have had epochs of growth during which they were bounded by two surface forms: normal {111} facets together with non-flat surfaces of mean {100} orientation (‘cuboid’ surfaces). Differences of lattice imperfection content in octahedral and cuboid growth sectors (i. e. in regions that ha…
Vertex correction calculations for an electron gas
A straightforward attempt to estimate the influence of the first vertex correction for a homogeneous electron gas is made. The approximation scheme is also tested on a solvable model of a core electron coupled to an electron gas.
Theory of photoconductivity in amorphous semiconductors containing relatively narrow trap bands
For a constant rate G of generation of electron-hole pairs, lg J ph (J ph is the photocurrent) increases as T -1 at high temperatures and reaches a maximum value of J m at T=T m . Thereafter, lg J ph decreases as T -1 with further decrease in temperature and finally, at low temperatures, J ph becomes independent of te…
Magnetic interactions in gadolinium orthochromite, GdCrO3
The magnetic properties of the distorted perovskite GdCrO 3 have been investigated by magnetic moment measurements in the temperature range below 100K and specific heat measurements below 10K. Measurements show that the canting of the Cr 3+ ions from a simple antiferromagnetic alignment is due to antisymmetric exchang…
Grain-size effects on properties of some ferroelectric ceramics
Hot-pressed ceramics of the lead titanate zirconate system with different grain sizes were prepared and some of their electrical properties measured. The values of the dielectric and piezoelectric properties were analysed together with information on barium titanate ceramics already published in the literature. Many s…
Backward Scattering in the One-Dimensional Electron Gas
An exact solution to the one-dimensional electron gas with a particular attractive-interaction strength for scattering across the Fermi "surface" is given. It is shown that conductivity enhancement occurs for physically interesting values of the coupling constants. Scaling arguments are advanced to demonstrate that th…
Dynamic viscoelastic properties of unsintered polytetrafluoroethylene
Abstract The molecular motion of unsintered polytetrafluoroethylene (PTFE) was studied by dynamic viscoelastic measurements. From results for variously heat treated suspension polymerized (molding powder) PTFE, the following conclusions are drawn. Molding powder, as received, has a high degree of crystallinity accordi…
Are vashegyite and kingite hydrous aluminum phyllophosphates with kaolinite-type structures ?
Summary In contrast with some other hydrous aluminum phosphates, vashegyite is crystalline. Simultaneous application of several assumptions leads to the hypothesis that it has a structure analogous to that of kaolinite, and thus contains tetrahedral sheets, n [X 2 O 5 ], where X is both P and H 3 (in lieu of Si). Thus…
A Modification of the Almon Distributed Lag
This article modifies the Almon polynomial distributed lag to allow for a lag of infinite length. Estimation of the model is considered, and an empirical example is given to illustrate the usefulness of the model
POLYMORPHISM IN THE DESMID MICRASTERIAS PINNATIFIDA AND ITS TAXONOMICAL IMPLICATIONS1
SUMMARY A case of polymorphism in the desmid Micrasterias pinnatifida (Kütz.) Ralfs is described. It is based on material collected from the overflow channel of a dam in Caeté, Minas Gerais State. After careful examination of nearly 500 specimens, 26 different morphological expressions of the alga were found which led…