126 resultados para Absolute, The.


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A series of ten cis-dihydro-diol metabolites has been obtained by bacterial biotransformation of the corresponding 1,4-disubstituted benzene substrates using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). Their enantiomeric excess (ee) values have been established using chiral stationary phase HPLC and H-1 NMR spectroscopy. Absolute configurations of the majority of cis-dihydrodiols have been established using stereochemical correlation and X-ray crystallography and the remainder have been tentatively assigned using NMR spectroscopic methods but finally confirmed by circular dichroism (CD) spectroscopy. These configurational assignments support and extend the validity of an empirical model, previously used to predict the preferred stereochemistry of TDO-catalysed cis-dihydroxylation of ten 1,4-disubstituted benzene substrates, to more than twenty-five examples.

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A combination method of ozonolysis and chiral stationary phase (CSP)-GC-MS analysis has been developed to determine the enantiopurity values and absolute configurations of a range of alkaloid and coumarin hemiterpenoids derived from C- and O-prenyl epoxides.

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A curved crystal spectrometer in Johann configuration has been implemented on MAST to obtain values for electron temperature, ion temperature and toroidal velocity. The spectrometer is used to examine medium Z impurities in the soft x-ray region by utilising a Silicon (111) crystal, bent using a 4 pin bending jig, and a CCD detector (Deltat=8 ms). Helium-like Argon emissions from 3.94 to 4.00 Angstrom have been examined using a crystal radius of 859.77 mm. The Bragg angle and crystal radius can be adjusted with relative ease. The spectrometer can be scanned toroidally and poloidally to include a radial view which facilitates absolute velocity measurements by assuming radial velocity =0. Doppler shifts of 2.3x10(-5) Angstrom (1.8 kms(-1)) can be measured. The line of sight is shared with a neutral particle analyzer, which enables in situ ion temperature comparisons. Ray tracing has been used for the development of new imaging spectrometers, using spherical/toroidal crystals, planned to be implemented on MAST. (C) 2004 American Institute of Physics.

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An absolute erythrocytosis is present when the red cell mass is raised and the haematocrit is elevated above prescribed limits. Causes of an absolute erythrocytosis can be primary where there is an intrinsic problem in the bone marrow and secondary where there an event outside the bone marrow driving erythropoiesis. This can further be divided into congenital and acquired causes. There remain an unexplained group idiopathic erythrocytosis. Investigation commencing with thorough history taking and examination and then investigation depending on initial features is required. Clear simple criteria for polycythaemia vera are now defined. Those who do not fulfil these criteria require further investigation depending on the clinical scenario and initial results. The erythropoietin level provides some guidance as to the direction in which to proceed and the order and extent of investigation necessary in an individual patient. It should thus be possible to make an accurate diagnosis in the majority of patients.

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Measurements on the dissociative recombination (DR) of protonated acrylonitrile, CH2CHCNH+, have been performed at the heavy ion storage ring CRYRING located in the Manne Siegbahn Laboratory in Stockholm, Sweden. It has been found that at~2meV relative kinetic energy about 50% of the DR events involve only ruptures of X–H bonds (where X=C or N)while the rest leads to the production of a pair of fragments each containing two heavy atoms (alongside H and/or H2). The absolute DR cross section has been investigated for relative kinetic energies ranging from ~1 meV to 1 eV. The thermal rate coefficient has been determined to follow the expression k(T) = 1.78 × 10-6 (T/300)-0.80 cm3 s-1 for electron temperatures ranging from ~10 to 1000 K. Gas-phase models of the nitrile chemistry in the dark molecular cloud TMC-1 have been run and results are compared with observations. Also, implications of the present results for the nitrile chemistry of Titan’s upper atmosphere are discussed.

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The two-photon resonances of atomic hydrogen (? = 2 × 205.1 nm), atomic nitrogen (? = 2 × 206.6 nm) and atomic oxygen (? = 2 × 225.6 nm) are investigated together with two selected transitions in krypton (? = 2×204.2 nm) and xenon (? = 2×225.5 nm). The natural lifetimes of the excited states, quenching coefficients for the most important collisions partners, and the relevant ratios of the two-photon excitation cross sections are measured. These data can be applied to provide a calibration for two-photon laser-induced fluorescence measurements based on comparisons with spectrally neighbouring noble gas resonances.

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The potential of laser-induced fluorescence spectroscopy of atoms is reviewed with emphasis on the determination of absolute densities. Examples of experiments with single-photon and two-photon excitation are presented. Calibration methods applicable with the different schemes are discussed. A new method is presented that has the potential to allow absolute measurement in plasmas of elevated pressure where collisional depletion of the excited state is present.

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The atmospheric pressure plasma jet is a capacitively coupled radio frequency discharge (13.56 MHz) running with a high helium flux (2m3 h-1) between concentric electrodes. Small amounts (0.5%) of admixed molecular oxygen do not disturb the homogeneous plasma discharge. The jet effluent leaving the discharge through the ring-shaped nozzle contains high concentrations of radicals at a low gas temperature—the key property for a variety of applications aiming at treatment of thermally sensitive surfaces. We report on absolute atomic oxygen density measurements by two-photon absorption laser-induced fluorescence (TALIF) spectroscopy in the jet effluent. Calibration is performed with the aid of a comparative TALIF measurement with xenon. An excitation scheme (different from the one earlier published) providing spectral matching of both the two-photon resonances and the fluorescence transitions is applied.

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The complex dynamics of radio-frequency driven atmospheric pressure plasma jets is investigated using various optical diagnostic techniques and numerical simulations. Absolute number densities of ground state atomic oxygen radicals in the plasma effluent are measured by two-photon absorption laser induced fluorescence spectroscopy (TALIF). Spatial profiles are compared with (vacuum) ultra-violet radiation from excited states of atomic oxygen and molecular oxygen, respectively. The excitation and ionization dynamics in the plasma core are dominated by electron impact and observed by space and phase resolved optical emission spectroscopy (PROES). The electron dynamics is governed through the motion of the plasma boundary sheaths in front of the electrodes as illustrated in numerical simulations using a hybrid code based on fluid equations and kinetic treatment of electrons.

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We report the discovery of a periodic modulation in the optical lightcurve of the candidate ultracompact X-ray binary 4U 1822-000. Using time-resolved optical photometry taken with the William Herschel Telescope we find evidence for a sinusoidal modulation with a semi-amplitude of 8 per cent and a period of 191 min, which is most likely close to the true orbital period of the binary. Using the van Paradijs & McClintock relation for the absolute magnitude and the distance modulus allowing for interstellar reddening, we estimate the distance to 4U 1822-000 to be 6.3 kpc. The long orbital period casts severe doubts on the ultracompact nature of 4U 1822-000.

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Absolute measurements have been made of single-electron charge-exchange cross sections of H+, He+, and He2+ in H2O and CO2 in the energy range 0.3-7.5 keV amu(-1). Collisions of this type occur in the interaction of solar wind ions with cometary gases and have been observed by the Giotto spacecraft using the Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during a close encounter with comet Halley in 1986. Increases in the He+ ion density, and in the He2+ to H+ density ratio were reported by Shelley et al, and Fuselier et al. and were explained by charge exchange. However, the lack of reliable cross sections for this process made interpretation of the data difficult. New cross sections are presented and discussed in relation to the Giotto observations.

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We have used XUV lasers to make absolute measurements of the photoabsorption coefficient of Al at energies just below that of the L3 absorption edge at 72.7 eV. Transmission measurements at photon energies of 53.7 and 63.3 eV have been made using Ne-like Ni and Ge XUV lasers. The XUV laser output was recorded in first and second orders using a flat-field spectrometer. Al foils with steps of various thicknesses were placed over the first order diffracted signal, while the second order diffraction was used to monitor the beam profile at each position. The transmission data agree extremely well with the original measurements at these wavelengths made by Henke and co-workers (Henke B L, Gullikson E M and Davis J C 1993 At. Data Nucl. Data Tables 54 18 1), but are in conflict with subsequent measurements which are currently in common use (Gullikson E M, Denham P, Mrowka S and Underwood J H 1994 Phys. Rev. B 49 16 283). The exact values of the absorption coefficients in this region of the spectrum have significant implications for the diagnosis of the energy and intensity output of XUV lasers.

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Absolute atomic oxygen ground state densities in a radio-frequency driven atmospheric pressure plasma jet, operated in a helium-oxygen mixture, are determined using diagnostic based modeling. One-dimensional numerical simulations of the electron dynamics are combined with time integrated optical emission spectroscopy. The population dynamics of the upper O 3p 3P (l=844 nm) atomic oxygen state is governed by direct electron impact excitation, dissociative excitation, radiation losses, and collisional induced quenching. Absolute values for atomic oxygen densities are obtained through comparison with the upper Ar 2p1 (l=750.4 nm) state. Results for spatial profiles and power variations are presented and show excellent quantitative agreement with independent two-photon laser-induced fluorescence measurements.

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Using two complementary experimental methods, we have measured partial (mass-resolved) cross-sections for dissociative electron attachment to the molecule trifluoromethyl sulfurpentafluoride (SF5CF3) at the gas temperature T-G = 300 K over a broad range of electron energies (E = 0.001-12 eV). The absolute scale for these cross-sections was obtained with reference to the thermal (T = 300 K) rate coefficient for anion formation (8.0(3) x 10(-8) cm(3) s(-1)). Below 1 eV, SF5- is the dominant product anion and formed through the lowest anion state which cuts the neutral SF5CF3 potential close to the S-C equilibrium distance. The highly resolved laser photoelectron attachment data exhibit a downward Wigner cusp at 86meV, indicating that the nu(4)(alpha(1)) vibrational mode is important for the primary attachment dynamics. Both SF5- and F- anions are formed with similar yields through the first excited resonance located near 3.6eV. Towards higher energies, the anions CF3-, SF4-, and SF3- are also produced. Summation of the partial cross-sections yields a total absolute cross-section for anion formation over the energy range 0.001-12 eV. This is used to calculate the dependence of the rate coefficient for dissociative electron attachment over a broad range of electron temperatures for the fixed gas temperature T-G = 300 K; good agreement is found between the calculated values and those obtained in a drift tube experiment. In addition to the experimental work, semiempirical R-matrix calculations have been Carried out for the energy dependence of the cross-section for SF5- formation. The experimental findings are semi-quantitatively recovered. (C) 2008 Elsevier B.V. All rights reserved.

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Objectives: Cilostazol improves walking distance in peripheral arterial disease (PAD) patients. The study objectives were to assess the effects of cilostazol on walking distance, followed by the additional assessment of cilostazol on exercise-induced ischaemiaereperfusion injury in such patients.

Methods: PAD patients were prospectively recruited to a double-blinded, placebo-controlled trial. Patients were randomised to receive either cilostazol 100 mg or placebo twice a day. The primary end-point was an improvement in walking distance. Secondary end-points included the assessment of oxygen-derived free-radical generation, antioxidant consumption and other markers of the in?ammatory cascade. Initial and absolute claudication distances (ICDs and ACDs, respectively) were measured on a treadmill. In?ammatory response was assessed before and 30 min post-exercise by measuring lipid hydroperoxide, ascorbate, atocopherol, b-carotene, P-selectin, intracellular and vascular cell-adhesion molecules (I-CAM and V-CAM), thromboxane B2 (TXB2), interleukin-6, interleukin-10, high-sensitive C-reactive protein (hsCRP), albuminecreatinine ratio (ACR) and urinary levels of p75TNF receptor. All tests were performed at baseline and 6 and 24 weeks.

Results: One hundred and six PAD patients (of whom 73 were males) were recruited and successfully randomised from December 2004 to January 2006. Patients who received cilostazol demonstrated a more signi?cant improvement in the mean percentage change from baseline in ACD (77.2% vs. 26.6% at 6 weeks, pZ0.026 and 161.7% vs. 79.0% at 24 weeks, pZ0.048) as compared to the placebo. Cilostazol reduced lipid hydroperoxide levels compared to a placebo-related increase before and after exercise (6 weeks: pre-exercise: 11.8% vs.