A meta-heuristic approach to parallel code generation

The efficient generation of parallel code for multi-processor environments, is a large and complicated issue. Attempts to address this problem have always resulted in significant input from users. Because of constraints on user knowledge and time, the automation of the process is a promising and practically important research area. In recent years heuristic approaches have been used to capture available knowledge and make it available for the parallelisation process. Here, the introduction of a novel approach of neural network techniques is combined with an expert system technique to enhance the availability of knowledge to aid in the automatic generation of parallel code.

Degradation, cyclic adenosine monophosphate production, insulin secretion, and glycemic effects of two novel N-terminal Ala(2)-substituted analogs of glucose-dependent insulinotropic polypeptide with preserved biological activity in vivo

Glucose-dependent insulinotropic polypeptide (GIP) has significant potential in diabetes therapy due to its ability to serve as a glucose-dependent activator of insulin secretion. However, its biological activity is severely compromised by the ubiquitous enzyme dipeptidylpeptidase IV (DPP IV), which removes the N-terminal Tyr(1)-Ala(2) dipeptide from GIP. Therefore, 2 novel N-terminal Ala(2)-substituted analogs of GIP, with Ala substituted by 2-aminobutyric acid (Abu) or sarcosine (Sar), were synthesized and tested for metabolic stability and biological activity both in vitro and in vivo. Incubation with DPP IV gave half-lives for degradation of native GIP, (Abu(2))GIP, and (Sar(2))GIP to be 2.3, 1.9, and 1.6 hours, respectively, while in human plasma, the half-lives were 6.2, 7.6, and 5.4 hours, respectively. In Chinese hamster lung (CHL) cells expressing the cloned human GIP receptor, native GIP, (Abu(2))GIP, and (Sar(2))GIP dose-dependently stimulated cyclic adenosine monophosphate (camp) production with EC50 values of 18.2, 38.5, and 54.6 nmol/L, respectively. In BRIN-BD11 cells, both (Abu(2))GIP and (Sar(2))GIP (10(-13) to 10(-8) mol/L) dose-dependently stimulated insulin secretion with significantly enhanced effects at 16.7 mmol/L compared with 5.6 mmol/L glucose. In obese diabetic (ob/ob) mice, GIP and (Sar(2))GIP significantly increased (1.4-fold to 1.5-fold; P <.05) plasma insulin concentrations, whereas (Abu(2))GIP exerted only minor effects. Changes in plasma glucose were small reflecting the severe insulin resistance of this mutant. The present data show that substitution of the penultimate N-terminal Ala(2) in GIP by Abu or Sar results in analogs with moderately reduced metabolic stability and biological activity in vitro, but with preserved biological activity in vivo. (C) 2003 Elsevier Inc. All rights reserved.

Cyclic AMP production and insulin releasing activity of synthetic fragment peptides of glucose-dependent insulinotropic polypeptide

Synthetic fragment peptides of glucose-dependent insulinotropic polypeptide (GIP) were evaluated for their ability to elevate cellular cAMP production and stimulate insulin secretion. In GIP receptor transfected CHL cells, GIP(4-42) and GIP(17-30) dose-dependently inhibited GIP-stimulated cAMP production (40 +/- 8%; p <0.01 and 15 +/- 6%; p <0.05, respectively), while GIP(1-16) exerted very weak agonist effects on cAMP production. In the clonal pancreatic beta-cell line, BRIN-BD11, GIP(1-16) demonstrated weak insulin releasing activity compared with native GIP. In contrast, GIP(4-42) and GIP (17-30) weakly antagonized the insulin releasing activity of the native peptide (23 +/- 6%; p <0.05 and 11 +/- 3%, respectively). These data demonstrate the critical role of the N-terminus and the involvement of regions of the C-terminal domain in generating full biological potency of GIP.

Voltammetry of oxygen in the room-temperature ionic liquids 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide and hexyltriethylammonium bis((trifluoromethyl)sulfonyl)imide: One-electron reduction to form superoxide. Steady-state and transient behavior in the same cyclic voltammogram resulting from widely different diffusion coefficients of oxygen and superoxide

The electrochemical reduction of oxygen in two different room-temperature ionic liquids, 1-ethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide ([EMIM][N(Tf)(2)]) and hexyltriethylammonium bis((trifluoromethyl)sulfonyl)imide ([N-6222][N(Tf)(2)]) was investigated by cyclic voltammetry at a gold microdisk electrode. Chronoamperometric measurements were made to determine the diffusion coefficient, D, and concentration, c, of the electroactive oxygen dissolved in the ionic liquid by fitting experimental transients to the Aoki model. [Aoki, K.; et al. J. Electroanal. Chem. 1981, 122, 19]. A theory and simulation designed for cyclic voltammetry at microdisk electrodes was then employed to determine the diffusion coefficient of the electrogenerated superoxide species, O-2(.-), as well as compute theoretical voltammograms to confirm the values of D and c for neutral oxygen obtained from the transients. As expected, the diffusion coefficient of the superoxide species was found to be smaller than that of the oxygen in both ionic liquids. The diffusion coefficients of O-2 and O-2(.-) in [N-6222][N(Tf)(2)], however, differ by more than a factor of 30 (D-O2 = 1.48 x 10(-10) m(2) s(-1), DO2.- = 4.66 x 10(-12) m(2) s(-1)), whereas they fall within the same order of magnitude in [EMIM][N(Tf)(2)] (D-O2 = 7.3 x 10(-10) m(2) s(-1), DO2.- = 2.7 x 10(-10) m(2) s(-1)). This difference in [N-6222][N(Tf)(2)] causes pronounced asymmetry in the concentration distributions of oxygen and superoxide, resulting in significant differences in the heights of the forward and back peaks in the cyclic voltammograms for the reduction of oxygen. This observation is most likely a result of the higher viscosity of [N-6222][N(Tf)(2)] in comparison to [EMIM][N(Tf)(2)], due to the structural differences in cationic component.

SDSS J150722.30+523039.8: a cataclysmic variable formed directly from a detached white dwarf/brown dwarf binary?

We present high-speed, three-colour photometry of the eclipsing cataclysmic variable SDSS J150722.30+523039.8 (hereafter SDSS J1507). This system has an orbital period of 66.61 min, placing it below the observed `period minimum' for cataclysmic variables. We determine the system parameters via a parametrized model of the eclipse fitted to the observed lightcurve by ?2 minimization. We obtain a mass ratio of q = 0.0623 +/- 0.0007 and an orbital inclination . The primary mass is Mw = 0.90 +/- 0.01Msolar. The secondary mass and radius are found to be Mr = 0.056 +/- 0.001Msolar and Rr = 0.096 +/- 0.001Rsolar, respectively. We find a distance to the system of 160 +/- 10pc. The secondary star in SDSS J1507 has a mass substantially below the hydrogen burning limit, making it the second confirmed substellar donor in a cataclysmic variable. The very short orbital period of SDSS J1507 is readily explained if the secondary star is nuclearly evolved, or if SDSS J1507 formed directly from a detached white dwarf/brown dwarf binary. Given the lack of any visible contribution from the secondary star, the very low secondary mass and the low HeI ?6678/Ha emission-line ratio, we argue that SDSS J1507 probably formed directly from a detached white dwarf/brown dwarf binary. If confirmed, SDSS J1507 will be the first such system identified. The implications for binary star evolution, the brown dwarf desert and the common envelope phase are discussed.

A Brown Dwarf Mass Donor in an Accreting Binary

A long-standing and unverified prediction of binary star evolution theory is the existence of a population of white dwarfs accreting from substellar donor stars. Such systems ought to be common, but the difficulty of finding them, combined with the challenge of detecting the donor against the light from accretion, means that no donor star to date has a measured mass below the hydrogen burning limit. We applied a technique that allowed us to reliably measure the mass of the unseen donor star in eclipsing systems. We were able to identify a brown dwarf donor star, with a mass of 0.052 ± 0.002 solar mass. The relatively high mass of the donor star for its orbital period suggests that current evolutionary models may underestimate the radii of brown dwarfs.

Time-resolved optical photometry of the ultracompact binary 4U 0614+091

We present a detailed optical study of the ultracompact X-ray binary 4U 0614+091. We have used 63 hr of time-resolved optical photometry taken with three different telescopes (IAC80, NOT, and SPM) to search for optical modulations. The power spectra of each data set reveals sinusoidal modulations with different periods, which are not always present. The strongest modulation has a period of 51.3 minutes, a semiamplitude of 4.6 mmag, and is present in the IAC80 data. The SPM and NOT data show periods of 42 minutes and 64 minutes, respectively, but with much weaker amplitudes, 2.6 mmag and 1.3 mmag, respectively. These modulations arise from either X-ray irradiation of the inner face of the secondary star and/or a superhump modulation from the accretion disk, or quasiperiodic modulations in the accretion disk. It is unclear whether these periods/quasi-periodic modulations are related to the orbital period; however, the strongest period of 51.3 minutes is close to earlier tentative orbital periods. Further observations taken over a long baseline are encouraged.

The effect of star-spots on eclipse timings of binary stars

We investigate the effects that star-spots have on the light curves of eclipsing binaries, and in particular how they may affect the accurate measurement of eclipse timings. Concentrating on systems containing a low-mass main-sequence star and a white dwarf, we find that if star-spots exhibit the Wilson depression they can alter the times of primary eclipse ingress and egress by several seconds for typical binary parameters and star-spot depressions. In addition, we find that the effect on the eclipse ingress/egress times becomes more profound for lower orbital inclinations. We show how it is possible, in principle, to determine estimates of both the binary inclination and the depth of the Wilson depression from light curve analysis.

The cyclic “silver-diphos” motif [Ag2(-diphosphine)2]2+ as a synthon for building up larger structure structures

The dinuclear, cyclic structural motif [Ag-2(diphosphine)(2)](2+), here termed the

1,2-Cyclic sulfite and sulfate furanoside diesters: improved syntheses and stability

The facile syntheses of 1,2- and 3,5-cyclic sulfite and sulfate furanoside diesters were conducted in molecular solvents and ionic liquids in the presence of immobilised morpholine. Molecular solvents and ionic liquids performed similarly with regards to overall yields. However, the use of ILs allowed for the reactions to be carried out under atmospheric conditions and showed good recyclability. Additionally, increases in product stability was achieved in ILs over organic solvents, in particular, in bis{(trifluoromethanesulfonyl)imide) and trispentafluoro-ethyltrifluorophosphate-based ionic liquids, which were also excellent media to control the hydrolysis of thionyl chloride and sulfuryl chloride. (C) 2009 Elsevier Ltd. All rights reserved.

Ligand differentiated complementary Rh-catalyst systems for the enantioselective desymmetrization of meso-cyclic anhydrides

Two distinct systems for the rhodium-catalyzed enantioselective desymmetrization of meso-cyclic anhydrides have been developed. Each system has been optimized and are compatible with the use of in situ prepared organozinc reagents. Rhodium/PHOX species efficiently catalyze the addition of alkyl nucleophiles to glutaric anhydrides, while a rhodium/phosphoramidite system is effective in the enantioselective arylation of succinic and glutaric anhydrides.

Temperature-Driven Mixing-Demixing Behavior of Binary Mixtures of the Ionic Liquid Choline Bis(trifluoromethylsulfonyl)imide and Water

The ionic liquid (2-hydroxyethylammonium)trimethylammonium) bis(trifluoromethylsulfonyl)imide (choline bistriflimide) was obtained as a supercooled liquid at room temperature (melting point = 30 degrees C). Crystals of choline bistriflimide suitable for structure determination were grown from the melt in situ on the X-ray diffractometer. The choline cation adopts a folded conformation, whereas the bistriflimide anion exhibits a transoid conformation. The choline cation and the bistriflimide anion are held together by hydrogen bonds between the hydroxyl proton and a sulfonyl oxygen atom. This hydrogen bonding is of importance for the temperature-dependent solubility proper-ties of the ionic liquid. Choline bistriflimide is not miscible with water at room temperature, but forms one phase with water at temperatures above 72 degrees C (equals upper critical solution temperature). H-1 NMR studies show that the hydrogen bonds between the choline cation and the bistriflimide anion are substantially weakened above this temperature. The thermophysical properties of water-choline bistriflimide binary mixtures were furthermore studied by a photopyroelectric technique and by adiabatic scanning calorimetry (ASC). By photothermal analysis, besides highly accurate values for the thermal conductivity and effusivity of choline bistriflimide at 30 degrees C, the detailed temperature dependence of both the thermal conductivity and effusivity of the upper and lower part of a critical water-choline bistriflimide mixture in the neighborhood of the mixing-demixing phase transition could be determined with high resolution and accuracy. Together with high resolution ASC data for the heat capacity, experimental values were obtained for the critical exponents alpha and beta, and for the critical amplitude ratio G(+)/G(-). These three values were found to be consistent with theoretical expectations for a three dimensional Ising-type of critical behavior of binary liquid mixtures.