Structure of neutron-rich Be and C isotopes

The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei ⁹Be or ¹⁰Be, respectively. Molecular rotational bands up to high excitation energies are observed with ⁹Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with ¹⁰Be as the core. For ¹¹Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2⁺, 5/2^?, and 3/2^?, respectively. Furthermore, we have studied particle-hole states of ¹⁶C using the ¹³C(¹²C, ⁹C)¹⁶C reaction and found 14 previously unknown states. Using the ¹²C(¹²C, ⁹C)¹⁵C reaction, five new states were observed for ¹⁵C.     

Fluid and diffusion limits for transient sojourn times of processor sharing queues with time varying rates

We provide an approximate analysis of the transient sojourn time for a processor sharing queue with time varying arrival and service rates, where the load can vary over time, including periods of overload. Using the same asymptotic technique as uniform acceleration as demonstrated in [12] and [13], we obtain fluid and diffusion limits for the sojourn time of the M_t/M_t/1 processor-sharing queue. Our analysis is enabled by the introduction of a “virtual customer” which differs from the notion of a “tagged customer” in that the former has no effect on the processing time of the other customers in the system. Our analysis generalizes to non-exponential service and interarrival times, when the fluid and diffusion limits for the queueing process are known.     

Perfluorophenyl derivatives of the elements XXVIII. Some reactions of fluoro-aromatic acetylenes

Reactions between caesium fluoride, bromine, palladium chloride, triiron dodecacarbonyl, dicobalt octacarbonyl, nickelocene, cyclopentadienylmanganese tricarbonyl or decarborane with, acetylenes containing one highly fluorinated aromatic group are described. The products mainly resembled those obtained from analogous experiments involving diphenylacetylene, although in the case of the PdCl₂ reaction no intermediate derivatives could be isolated.     

The crystal and molecular structure of dodecafluorotriphenylene, C18F12

The dodecafluorotriphenylene molecule is considerably distorted from planarity by steric interactions between the “ortho” fluorine atoms which approach to within 2.41 Å of each other (or about 0.3 Å closer than the sum of the van der Waals radii for two fluorine atoms, 2.70 Å).     

Tests for liquid chromatographs

Summary The paper describes tests for liquid chromatographs to assess the autosampler and pump flow rate precision; suitability of the instrument for normal phase chromatography; UV detector performance; and external band broadening characteristics. Tests for mixing and proportioning characteristics of solvent pumps and performance of diode array detectors are also considered. These tests are designed to evaluate the performance of both newly released liquid chromatography equipment and equipment already in operation. Data from evaluations carried out by instrument manufacturer’s and suppliers is reported and discussed. This data offers specifications to a common format for initial selection of instruments prior to purchase.     

Capillary column gas chromatographic method using electron-capture detection for the simultaneous determination of nicardipine and its pyridine metabolite II in plasma

A rapid, specific and direct method based on capillary column gas chromatography with electron-capture detection is described for the simultaneous determination of nicardipine, a new calcium antagonist, and its pyridine metabolite II in human plasma. In this method, the nicardipine, its pyridine metabolite II and internal standard are extracted from the plasma and then partially purified by acid-base partitioning prior to the final injection onto the capillary column gas chromatograph for quantification by means of an electron-capture detector. The quantification limit of the method is 1 ng/ml of plasma for both nicardipine and its pyridine metabolite II. The coefficients of variation for nicardipine and the pyridine metabolite II at concentrations of 1-50 ng/ml are less than 7% and less than 9% (n = 4), respectively. The method has been validated against a previously developed high-performance liquid chromatographic method (sensitivity 5 ng/ml).     

The crystal and molecular structures of bis (pentafluorophenyl)disulphide and bis(pentafluorophenyl)diselenide

The structures of (C₆F₅)₂S₂ and (C₆F₅)₂Se₂ have been determined by single crystal, X-ray diffraction techniques. The compounds are isostructural although the molecules are packed differently in the crystal in comparison with their phenyl analogues. Important bond lengths and angles are: SS, 2.059(4)Å; SeSe, 2.319(4)Å; SC, 1.770Å; SeC, 1.910(15)Å; SSC, 101.3(3)°; SeSeC, 98.8(1)°.     

Determination of carbaryl as its primary metabolite, 1-naphthol, by reversed-phase high-performance liquid chromatography with fluorometric detection

Carbaryl and its hydrolysis product, 1-naphthol, are determined simultaneously, and in a mixture of other pesticides, by reversed-phase high-performance liquid chromatography (HPLC). Fluorometric detection affords a higher degree of selectivity than absorbance detection, while providing detection limits of 1.0 ng ml(-1) and 1.4 mg ml(-1) for 1-naphthol and carbaryl, respectively. The described method requires no enrichment of samples and includes a simple hydrolysis step. Additionally, enhancement of fluorescence detection signal intensity is explored through HPLC solvent composition effects as well as through formation of cyclodextrin inclusion complexes. The method described in this report is a selective and fast alternative to the currently accepted U.S. Environmental Protection Agency (EPA) method of detection carbaryl in ground water.