Analysis of Open Discrete Time Queueing Networks: A Refined Decomposition Approach

This paper deals with approximate analysis methods for open queueing networks. External and internal flows from and to the nodes are characterized by renewal processes with discrete time distributions of their interarrival times. Stationary distributions of the waiting time, the queue size and the interdeparture times are obtained using efficient discrete time algorithms for single server (GI/G/1) and multi-server (GI/D/c) nodes with deterministic service. The network analysis is extended to semi-Markovian representations of each flow among the nodes, which include parameters of the autocorrelation function.     

Liquid chromatography electrospray mass spectrometry with variable fragmentor voltages gives simultaneous elemental and molecular detection of arsenic compounds

A single quadrupole high performance liquid chromatography electrospray mass spectrometry system with a variable fragmentor voltage facility was used in the positive ion mode for simultaneous recording of elemental and molecular mass spectral data for arsenic compounds. The method was applicable to the seven organoarsenic compounds tested: four arsenic-containing carbohydrates (arsenosugars), a quaternary arsonium compound (arsenobetaine), dimethylarsinic acid, and dimethylarsinoylacetic acid. It was not suitable for the two inorganic arsenic species arsenite and arsenate. In the case of arsenosugars, qualifying ion data for a characteristic common fragment (m/z 237) was also simultaneously obtained. The method was used to identify and quantify the major arsenosugars in crude extracts of two brown algae.     

Procedure for background estimation in energy-dispersive X-ray fluorescence spectra

A method for semi-automatic background estimation in energy-dispersive x-ray fluorescence spectra is outlined. Two cubic splines were investigated and the spline called the Butland interpolant was chosen for further investigation. Prior to the calculation of the spline, peak regions are set up, and suitable knots are defined outside the peak regions. To set up the peak regions, an automatic peak-search routine and a calibration equation are used. For a given peak, the latter relates the full width at half maximum (FWHM) to the peak centre. In turn, the size of the peak regions are defined by the FWHM multiplied by a constant given by the user. The method was tested on several types of spectra. It was found that the optimal size of the peak region decreased with increasing peak density. Reproducibility tests showed that the standard deviation of the summation of counts within a peak region and after background subtraction was less than would be expected from the counting statistics.     

Thioacetylacetone: structural and vibrational assignments.

Thioacetylacetone and its variously deuterated isotopomers have been investigated using electronic and vibrational spectroscopy combined with quantum chemical calculations. Thioacetylacetone is known for its photochromic properties, but the structures of the initial and final forms have been the subject of a long debate. Analysis of the IR spectra recorded in low-temperature argon and xenon matrices, room-temperature solutions, and in the gas phase has allowed us to establish the nature of the photochromic species and of its precursor. Similar to the case of another beta-thioxoketone, monothiodibenzoylmethane, the photo-product has been assigned to the nonchelated SH exo-rotamer of the (Z)-enethiol tautomeric form, whereas the dominant ground-state species corresponds to the chelated (Z)-enol tautomeric form. Detailed vibrational assignments have been proposed for both forms based on quantum chemical calculations and polarization experiments. In the case of the chelated (Z)-enol species prevailing in the ground state, a second-order perturbative anharmonic analysis at the B3LYP/cc-pVTZ level indicated strong anharmonic effects associated with the intramolecular hydrogen bond, leading to a shift of more than 600 cm-1 of the wavenumber of the OH-stretching vibration. A small fraction of the SH endo-rotameric chelated (Z)-enethiol form was also detected under unperturbed conditions. The (Z)-enethiol form can be converted into the (Z)-enol form by irradiation at 290 nm.     

Apparent Specific Volume Measurements of Poly(ethylene oxide), Poly(butylene oxide), Poly(propylene oxide), and Octadecyl Chains in the Micellar State as a Function of Temperature

Apparent specific densities of aqueous solutions of the diblock copolymers C18(EO)100, C18(EO)20, and (EO)92(BO)18 and the triblock copolymers (EO)25(PO)40(EO)25 and (EO)21(PO)47(EO)21 in the micellar state have been measured over a temperature range from 10 to 90 degrees C at concentrations between 1% and 5%, using an oscillating tube densitometer. From these measurements, apparent specific volumes of poly(ethylene oxide) (PEO), poly(propylene oxide) (PPO), poly(butylene oxide) (PBO), and octadecane in the micellar state have been determined. The composition of the block copolymers was checked by NMR spectroscopy. Results were compared with published data for the polymers and bulk values for octadecane, respectively. The apparent specific density of PEO chains in the dissolved state was also measured for PEG4600 solutions at different concentrations and compared with results in the micellar state. The results presented in the paper are crucial in connection with analysis and modeling of small-angle X-ray scattering (SAXS) data from polymer and block copolymer micellar systems. PEO and PPO have a relatively low apparent partial specific volume in water at low temperatures. It is associated with water molecules making strong hydrogen bonds with the oxygen atoms on the polymer backbone. These water molecules gradually become disordered when the temperature is increased and the polymer apparent specific volume increases. For PBO in the micellar cores of PBO-PEO block copolymer micelles and in PNiPAM microgels, pronounced temperature dependence with the same origin is also found. The application of the derived results for the apparent specific volume of PEO for deriving contrast factors is demonstrated and the results are used in the analysis of SAXS data for semidilute solutions of PEG4600 in a broad temperature range.     

高岭石吸附乙烯和苯的Delft分子力学研究

运用Ｄｅｌｆｔ分子力学（ＤＭＭ）程序及其粘土和共轭烯烃力场，计算研究了高岭石对乙烯和苯的吸附作用，探讨了吸附对粘土晶体和有机分子的结构、电荷分布和能量的影响，求得了高岭石吸附乙烯和苯的吸附热等重要物理量．     

Transannular reactions of two parallel 1,3-butadiynes: syntheses,structures, and reactions of 1-azacyclotetradeca-3,5,10,12-tetrayne derivatives

The synthesis of 1-alkyl and 1-aryl-1-azacyclotetradeca-3,5,10,12-tetraynes was achieved in a stepwise approach. The key intermediate was 1,13-dibromotrideca-2,4,9,11-tetrayne (18). Reaction with methyl- (19 a), ethyl- (19 b), isopropyl- (19 c), n-butyl- (19 d), and tert-butylamine (19 e) as well as aniline (19 f) and p-methoxyaniline (19 g) gave the corresponding 14-membered tetraynes 20 a-20 g. The ring inversion process of 20 b was studied by variable temperature (1)H NMR spectroscopy. From these measurements a value of 10.6 kcal mol(-1) was calculated for DeltaG(not equal). X-ray investigations on single crystals of 20 b, 20 c, and 20 f revealed the axial position for the substituent at each nitrogen atom. For 20 b we encountered the chair conformation, for 20 c both chair and boat conformations, and for 20 f the boat conformation in the solid state. The reaction of 20 c with concentrated HCl in ethanol yielded 2,10-dichloro-6-isopropyl-6-azatricyclo[9.3.0.0(4,8)]tetradeca-1(11),2,4(8),9-tetraene (25 c). Compound 25 c was oxidized by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) to 27 c. The structure of the latter was confirmed by X-ray investigations. The reaction of 20 c in aqueous HCl lead to the formation of 10-chloro-2-isopropyl-1,3,4,6,7,8-hexahydro-2H-benzo[g]isoquinolin-9-one (37 c). The structure of 37 c was verified by X-ray studies on single crystals.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-1-(Indanyloxymethyl) and <Emphasis Type="Italic">N</Emphasis>-1-(4-Hydroxybut-2-enyloxymethyl) Analogues of the HIV Drugs Emivirine and GCA-186

Summary. A series of Emivirine and GCA-186 analogues substituted at N-1 with indan-1-yloxymethyl (6a–6c) and indan-2-yloxymethyl (6d–6f) were synthesized by reaction of the corresponding bis(indanyloxy)methans with uracils having 5-ethyl or 5-isopropyl and 6-benzyl or 6-(3,5-dimethylbenzyl) substituents. A route to the corresponding N-1 substituted 4-hydroxybut-2-enyloxymethyl analogue was also devised. All newly synthesized compounds showed potent activity against wild-type HIV-1, the most active compound being 5-ethyl-1-(indan-1-yloxymethyl)-6-(3,5-dimethylbenzyl)uracil (6b), which was 50-fold more active than Emivirine.Present address: Chemistry Department, Faculty of Science, Tanta University, Tanta, EgyptA research center funded by The Danish National Research Foundation for studies on nucleic acid chemical biology     

The application of "click chemistry" for the decoration of 2(1H)-pyrazinone scaffold: generation of templates

The "click chemistry" approach has been explored on the 2-(1H)-pyrazinone scaffold for the generation of pharmacologically interesting heterocyclic moieties. Huisgen 1,3-dipolar cycloaddition has been evaluated as the key step for the construction of the 1,2,3-triazole ring at the C-3 position of 2-(1H)-pyrazinones. Two different pathways have been successfully evaluated: (1) via C-C or C-O linkage of the acetylenic part to the C-3 position of the 2-(1H)-pyrazinone scaffold or (2) via azide introduction in the C-3 position. The subsequent application of "click chemistry" resulted in the formation of hitherto unknown skeletons. Microwave irradiation has successfully been applied in different steps of the sequence.