Crystal structure of the rubidium salt of α, α-dinitroacetamide

Journal of Structural Chemistry -     

Determination of vitamins in food-matrix Standard Reference Materials

In recent years, the National Institute of Standards and Technology (NIST) has developed several food-matrix Standard Reference Materials (SRMs) characterized for vitamins and other organic nutrients. NIST uses several "modes" for assignment of analyte concentrations in SRMs, one of which includes the use of data provided by collaborating laboratories. Certification modes and liquid chromatographic methods that were used by NIST for value assignment of vitamin concentrations in recently introduced food-matrix SRMs are described in this paper. These materials and methods include vitamins D and E in coconut oil (SRM 1563) by gravimetry and multi-dimensional liquid chromatography (LC); vitamins A, E, and several B vitamins by reversed-phase LC and vitamin C by ion-exchange chromatography in infant formula (SRM 1846); and carotenoids and vitamins A and E by reversed-phase liquid chromatography in a baby food composite (SRM 2383).     

Finite aperiodic semigroups with commuting idempotents and generalizations

It is proved that any pseudovariety of finite semigroups generated by inverse semigroups, the subgroups of which lie in some proper pseudovariety of groups, does not contain all aperiodic semigroups with commuting idempotents. In contrast we show that every finite semigroup with commuting idempotents divides a semigroup of partial bijections that shares the same subgroups. Finally, we answer in the negative a question of Almeida as to whether a result of Stiffler characterizing the semidirect product of the pseudovarieties ofR-trivial semigroups and groups applies to any proper pseudovariety of groups.     

Line Positions and Intensities in the 2nu(2)/nu(4) Vibrational System of (14)NH(3) near 5-7 µm

Line positions and intensities belonging to the vibrational system 2nu(2)/nu(4) of ammonia (14)NH(3) are measured and analyzed between 1200 and 2200 cm(-1) in order to improve the molecular database. For this, laboratory spectra are obtained at 0.006 and 0.011 cm(-1) unapodized resolution and with 4% precisions for the intensities using Fourier transform spectrometers located at the Kitt Peak National Observatory and the Jet Propulsion Laboratory. The observed data contain transitions of the nu(4) fundamental band near 1626.276(1) and 1627.375(2) cm(-1) (for s and a inversion upper states, respectively) and the 2nu(2) overtone band near 1597.470(3) and 1882.179(5) cm(-1) (for s and a inversion states, respectively). A total of 2345 lines with J' 相似文献