Determination of retinyl palmitate (vitamin A) in fortified fluid milk by liquid chromatography: collaborative study

A liquid chromatographic (LC) method was developed for fast and simple measurement of retinyl palmitate (vitamin A) in fortified milk. Retinyl acetate internal standard was added to a test portion of milk followed by extraction into hexane. The hexane extract was analyzed by LC using a normal-phase silica gel column equilibrated with mobile phase (conditioned hexane-isopropanol, 99.85 + 0.15, v/v) about 1 h before injections. The retinyl palmitate concentration was calculated by using a relative response factor determined with calibration standards. In the collaborative study, 11 laboratories analyzed 13 pairs of fluid milk materials in blind duplicate. Twelve of the materials were composed of skim milk (< 0.5% fat), 1% fat milk, 2% fat milk, and 1% fat chocolate milk. Each material was fortified at 3 concentrations of retinyl palmitate of approximately 581 microg/L (1000 IU/qt), 1163 microg/L (2000 IU/qt), and 2236 microg/L (4000 IU/qt). The 13th material, unfortified skim milk, served as a matrix blank. Repeatability standard deviations (RSDr) without outliers ranged from 1.5 to 5.7% and reproducibility standard deviations (RSDR) without outliers ranged from 5.0 to 22.7%. cis-Isomers co-eluted with the predominant trans-retinyl palmitate isomer and were included in the results reported by all the collaborative laboratories. Endogenous long-chain esters from milk fat were also measured with the retinyl palmitate additive. The Study Director recommends that this method for determination of retinyl palmitate in fluid milk by LC be adopted First Action.     

Decoherence in josephson phase qubits from junction resonators

Although Josephson junction qubits show great promise for quantum computing, the origin of dominant decoherence mechanisms remains unknown. Improving the operation of a Josephson junction based phase qubit has revealed microscopic two-level systems or resonators within the tunnel barrier that cause decoherence. We report spectroscopic data that show a level splitting characteristic of coupling between a two-state qubit and a two-level system. Furthermore, we show Rabi oscillations whose "coherence amplitude" is significantly degraded by the presence of these spurious microwave resonators. The discovery of these resonators impacts the future of Josephson qubits as well as existing Josephson technologies.     

Approach for dislocation free GaN epitaxy

The characteristics of confined epitaxial growth are investigated with the goal of determining the contributing effects of mask attributes (spacing, feature size) and growth conditions (V/III ratio, pressure, temperature) on the efficiency of the approach for dislocation density reduction of GaN. In addition to standard (secondary electron and atomic force) microscopy, electron channeling contrast imaging (ECCI) is employed to identify extended defects over large (tens of microns) areas. Using this method, it is illustrated that by confining the epitaxial growth, high quality GaN can be grown with dislocation densities approaching zero.     

Effective range parameter ins-wave pion nucleon scattering

The effective range parameterb ^? for πN s-wave scattering is calculated from fixed-t dispersion relations, using experimental information for the imaginary parts. The result is compared with that of other calculations, based on Ward identities and phenomenological Lagrangians. It is pointed out that a direct determination ofb ^? from experimental data is not possible. Since the Δ-propagator is not unique, the Δ-exchange amplitudes are given for a one-parameter class of propagators (Appendix).     

Comparison of 14C-amino acid mixture and [35S]methionine labeling of cellular proteins from mouse fibroblast C3H10T1/2 cells by two-dimensional gel electrophoresis.

Total cellular proteins from mouse C3H10T1/2 fibroblasts were compared by two-dimensional (2-D) gel electrophoresis after radiolabeling with [35S]methionine (35S-Met) or 14C-amino acids (14C-AA). 35S-Met labeling of protein was three to four times greater than 14C-AA incorporation over a 24 h period. Automated comparative analysis of replicate fluorographs after 6, 12, and 24 h of labeling showed considerable homology between radiolabeling methods. More than 88% percent of 35S-Met and 14C-AA-labeled proteins were common at each time point. However, the total number of 35S-Met-labeled proteins dropped from 6 to 24 h while the number of 14C-AA-labeled proteins increased. Additionally, twenty-one proteins were uniquely labeled by 14C-AA that were not detectable by 35S-Met over the labeling period. Densitometric analysis showed that several 35S-Met and 14C-AA-labeled proteins exhibited time-related differences in radiolabel incorporation while most proteins remained relatively constant. Protein patterns of silver-stained gels from 6 to 24 h were highly registered and showed few qualitative differences. Proteins detected in radiolabeled gels were generally, but not always, found in silver-stained gels. Thus, 35S-Met appears better suited for short-term radiolabeling of cellular protein while more comprehensive labeling of protein occurs with 14C-AA during prolonged incubation of cell cultures under present experimental conditions.     

ππ scattering amplitudes within the sub-threshold triangle

The on-shell ππ scattering amplitudes within and on the boundary of the subthreshold triangle (0 ≤ s ≤ Σ, 0 ≤ t ≤ Σ, 0 ≤ u ≤ Σ ≡ 4μ²) are investigated. Interior Dispersion Relations, when combined with experimental ππ phase shifts, inelasticities, and scattering lengths, provide an almost perfect tool for this study. The general results obtained are in striking agreement with the chiral model of Weinberg.     

Conformational properties of α- and β-azabicyclane opiates. The effect of conformation on pharmacological activity

Conformational energy calculations using the MM 2 (molecular mechanics II) program are reported for diastereoisomeric α- and β-azabicyclanes (3-methyl-9-methoxy-9-phenyl-3-azabicyclo [3.3.1] nonanes) which are prototypical phenyl-axial and phenyl-equatorial opiates. After energy minimization, both compounds are found to prefer a chair–chair conformation of the piperidine and cyclohexane rings with two mirror image orientations of the phenyl and methoxyl groups. The calculations also indicate that the equilibrium conformations of the phenyl and methoxyl groups are very similar in the two diastereoisomers. A morphine-like conformation of the phenyl group was found to be very unfavorable because of a high barrier to rotation of the phenyl group. This does not have an apparent effect on opiate agonist properties, but does result in a significant weakening of the antagonist activity of the N-allyl derivative of α-azabicyclane. This is discussed in terms of a model for phenyl-axial and phenyl-equatorial opiate substrates which accounts for both similarities and differences in their structure–activity relationships. A detailed comparison is also made between the computed structures and those observed by x-ray crystallography with excellent agreement between the two.     

Lachnanthospirone,a dimeric 9-phenylphenalenone from the seeds of Lachnanthestinctoria ell.

The structure of lachnanthospirone [$\text{4}$] a novel dimeric pigment from $\text{Lachnanthes}$$\text{tinctoria}$ has been established from the X-ray crystal structure of a derivative [$\text{3}$] in which the spirolactone present in the natural product has been opened.     

Nature of luminescence and strain in gallium nitride nanowires

Photo- and cathodo-luminescence measurements of a variable-diameter ensemble of GaN nanowires revealed a diameter-dependent, spectral emission distribution between 350 nm and 850 nm. Spectral analysis indicated that wires with a diameter less than 400 nm were dominated by a yellow luminescence with a weaker near UV/violet emission also present. Examination of this ensemble showed that there was a general trend in the ratio of near-UV-to-yellow emission intensities with increasing nanowire diameter. Additionally, a broad green emission appears in the nanowires with a diameter above approximately 200 nm. A calculation based on the nanoheteroepitaxy model indicates that this diameter represents a transitional thickness where strain is relieved by defect formation mechanisms with a characteristic green emission.