Simultaneous mass spectrometric measurement of prostaglandins E1 (PGE1) and PGE2 with a deuterated internal standard

The use of (3,3,4,4-²H₄)PGE₂ as internal standard for the quantitative measurement of PGE₁ by gas chromatography-mass spectrometry is reported. A method for the simultaneous analysis of PGE₁ and PGE₂ is also described. The prostaglandins were analyzed by selected ion monitoring as the methyl ester-trimethylsilyl ether (ME-TMS) derivatives of PGB₁ and PGB₂, respectively. In all cases, a linear response over the range 1 to 70 ng (2.8 to 198 pmoles) was demonstrated. The use of this procedure is exemplified by its application to the PG analysis of sheep seminal vesicles. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable.     

Co-metabolism of citrate and maltose byLactobacillus brevis subsp.lindneri CB1 citrate-negative strain: effect on growth,end-products and sourdough fermentation

Growth, substrates and end-product formation of the maltose and citrate co-metabolization byLactobacillus brevis subsp.lindneri CB1 citrate-negative strain were initially studied in synthetic medium. Compared to maltose (19 g/l) fermentation, the co-metabolization of maltose (10 g/l) plus citrate (9 g/l) caused faster cell growth, increased the concentrations of lactic acid and especially of acetic acid (from 0.7 g/l to 2.9 g/l), produced succinic acid (0.5 g/l) and reduced ethanol synthesis. Highest activities of acetate kinase, the same of lactate dehydrogenase and a reduced alcohol dehydrogenase activity were detected in cytoplasmic extracts of cells growing on maltose plus citrate. The breakdown of citrate depended upon the continuous presence of maltose in the growth medium. Upon depletion of citrate, the cells continued through the normal maltose fermentation, having a diauxic metabolic curve as shown by impedance measurements. Concentrations of citrate from 3 g/l to 15 g/l led to increases of acetic acid from 1.25 g/l to 5.55 g/l. Since maltose was naturally present during sourdough fermentation, the addition of 9 g citrate per kg wheat dough enabled the co-metabolization of maltose and citrate byL. brevis subsp.lindneri CB1. Compared with traditional sourdough fermentation, faster cell growth, a higher acetic acid concentration and a reduced quotient of fermentation were obtained by co-metabolism.     

On some properties of very pure codes

Some results on synchronization and maximality of very pure codes are given.     

Structure and ion dynamics in AgI : Ag2B4O7 vitreous electrolytes

Compounds of the system (AgI)_x(Ag₂B₄O₇)_1?x can be thought of as a network made by an equal number of BO₃ and BO₄ groups containing silver iodide polyhedra. Partially crystalline compounds are obtained when the AgI molar fraction, x, is more than two times the Ag₂B₄O₇ fraction. For the same iodine concentration, the ionic conductivities of the AgI : Ag₂B₄O₇ glasses are comparable with those of other AgI : Ag-oxysalt glasses. However, their glass transition temperatures are substantially higher. With increasing silver iodine content, the physical properties which have been investigated approach smoothly the corresponding values expected for α-AgI. However, it is shown that Ag⁺ within the iodide polyhedra is not the unique current carrier and that a wide distribution of barrier heights exists in these glasses.     

Analysis of seismic testing motions with instantaneous response spectra

Synthetic multiple-frequency and single-frequency motions are analyzed for their adequacy to simulate a calculated seismic motion for seismic testing of nuclear power plant equipment. The analysis is performed by first comparing their time-independent response spectra and then comparing response spectra derived at an instant of time, that is, instantaneous response spectra. The results show that even though the time-independent response spectrum of the calculated motion is fully enveloped by that of a synthetic test motion, full enveloping is never obtained with the actual responses at any given time. Recommendations are given on practical test methods and type of test motions.     

Ultrahigh molecular weight polyethylene as used in articular prostheses (a molecular weight distribution study)

Currently there is widespread use of ultrahigh molecular weight polyethylene (UHMWPE) acetabular components in total joint replacement prostheses. What has been most surprising about the wear of UHMWPE under such circumstances is the occurrence of brittle fracture. Such fracture had not been observed in the usual engineering tests done in the laboratory on UHMWPE. It was only when prosthese which had been removed from patients were examined or run in hip joint simulators with serum or synovial fluid as the lubricant, that brittle fracture was encountered. The problem of environment-enhanced brittle fracture in plastics dates back to 1946. Interestingly, the phenomenon was first described in polyethylene. The prime variables involved are polymer molecular weight, sensitizing environment, stress filed, and temperature. Other things being equal, brittle behavior in polyethylene is extremely sensitive to the amount of low molecular weight polymer present. In the light of the foregoing we have studied the molecular weight distribution in six commercially available UHMWPE components. These were obtained from six different manufacturers. The specimens were characterized both on their bearing (wear) surfaces and in their interior bulk. The results obtained indicate that:

• 1 The UHMWPE components contain substantial amounts of low molecular weight polymer.
• 2 The UHMWPE components differ significantly in molecular weight distribution.
• 3 The UHMWPE components contain substantial amounts of crosslinked polymer.

     

Exfoliated/Intercalated Rubber/Organo‐Montmorillonite Nanocomposites: Preparation and Characterization

The preparation of new rubber based nanocomposites by using properly modified organophilic clays is described. A commercial organophilic montmorillonite containing a hydroxylated ammonium ion is reacted with LPBs. The reaction causes a decrease of the polarity of the clay and a great increase of the interlayer distance. The modified organoclays are successfully dispersed into rubber matrices (SBR or BR) by melt blending in an internal batch mixer. SAXS analyses and TEM micrographs revealed the formation of highly exfoliated nanocomposites containing intercalated stacks made of few lamellae.

     

Kinetics of the thermal dissociation of ZnO exposed to concentrated solar irradiation using a solar‐driven thermogravimeter in the 1800–2100 K range

The two‐step H₂O‐splitting thermochemical cycle based on the Zn/ZnO redox reactions is considered for solar H₂ production, comprising the endothermal dissociation of ZnO followed by the exothermal hydrolysis of Zn. A solar‐driven thermogravimeter, in which a packed‐bed of ZnO particles is directly exposed to concentrated solar radiation at a peak solar concentration ratio of 2400 suns while its weight loss is continuously monitored, was applied to measure the thermal dissociation rate in a set‐up closely approximating the heat and mass transfer characteristics of solar reactors. Isothermal thermogravimetric runs were performed in the range 1834–2109 K and fitted to a zero‐order Arrhenius rate law with apparent activation energy 361 ± 53 kJ mol^?1 K^?1 and frequency factor 14.03 × 10⁶ ± 2.73 × 10⁶ kg m^?2 s^?1. Application of L‘vov’s kinetic expression for solid decomposition along with a convective mass transport correlation yielded kinetic parameters in close agreement with those derived from experimental data. © 2009 American Institute of Chemical Engineers AIChE J, 2009