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421.
Established standard methods for analyzing semi-volatile pollutants by capillary gas chromatography are cumbersome, time-consuming, and expensive. With the longer term aim of replacing the sample preparation procedures with convenient concertrating and thermal desorption steps, thick film silicone rubber traps were constructed in a novel multi-channel configuration. Tests were performed to determine breakthrough volumes and thermal desorption characteristics for total transfer of the trap contents to a capillary column. Initial results are very promising. 相似文献
422.
Dr. Stefan Wagner M.Sc. Philipp Klose Dr. Vladimir Burlaka Dr. Kai Nörthemann Dr. Magnus Hamm Prof. Dr. Astrid Pundt 《Chemphyschem》2019,20(14):1890-1904
Metal−hydrogen (M−H) systems offer grand opportunities for studies on fundamental aspects of thermodynamics and kinetics. When the system size is reduced to the nanoscale, microstructural defects as well as mechanical stress affect the systems’ properties. This is contemplated for the model system of epitaxial niobium−hydrogen (Nb−H) thin films. Hydrogen absorption in metals commonly leads to lattice expansion which is hindered when the metal adheres to a flat rigid substrate. Consequently, high mechanical stress of about −10 GPa for 1 H/Nb are predicted, in theory. However, metals cannot yield such high stresses and respond with plastic deformation, commonly limiting measured stresses to −2 to −3 GPa for 100 nm Nb−H films. It will be shown that the coherency state changes with film thickness reduction, shifting the onset of plastic deformation to larger hydrogen concentrations. Below critical film thicknesses, plastic deformation is fully absent. The system then behaves purely elastic and ultra-high stress of about −10 (±2) GPa can be obtained. Arising stress controls the phase stability of M−H systems, and the coherency state strongly affects the nucleation and growth dynamics of the phase transition. In case of Nb−H thin films of less than 8 nm thickness the common phase transformation from the α-phase solid solution to the hydride phase is completely suppressed at 300 K. Related effects can be utilised to optimise metal−hydrides used in applications. 相似文献
423.
The effect of impermeable boundaries of arbitrary geometry on the apparent diffusion coefficient 总被引:1,自引:0,他引:1
Frøhlich AF Jespersen SN Ostergaard L Kiselev VG 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,194(1):128-135
The apparent diffusion coefficient (ADC) obtained from NMR measurements is modelled for diffusion in a compartment restricted by an impermeable boundary. For a given pulse sequence, the ADC can be determined from the connected velocity autocorrelation function (the second-order velocity cumulant), which we show can be expressed as a double surface integral over the boundary, involving the probability for molecules to diffuse from one boundary point to another. There is no restriction on the geometry of the boundary. This result allows a fast calculation of the ADC for an arbitrary time course of the diffusion-sensitizing gradient. Explicit examples are given for diffusion within three basic geometries for different pulse sequences. The ADCs measured with the Stejskal-Tanner pulse sequence and a more realistic pulse sequence with slice selection gradient and eddy current compensation are found to yield almost identical results. The application of the results are discussed in relation to determination of the microscopic structure of brain white matter. 相似文献
424.
Trifonov Lena Yurchenko Mariya Skjesol Astrid Cohen Guy Espevik Terje Korshin Edward E. Grøvdal Lene Melsæther Husebye Harald Gruzman Arie 《Molecular diversity》2022,26(4):2175-2188
Molecular Diversity - IFN-β is a cytokine that plays a significant role in the immune system. Inhibition of IFN-β might be used as a therapeutic approach to treat septic shock. A... 相似文献
425.
Lars Erik Eng Eibak Astrid Gjelstad Knut Einar Rasmussen Stig Pedersen-Bjergaard 《Journal of chromatography. A》2010,1217(31):5050-5056
Amitriptyline, citalopram, fluoxetine, and fluvoxamine were isolated by electro membrane extraction (EME) from 70 μl of untreated plasma (pH 7.4), through a supported liquid membrane (SLM) of 1-ethyl-2-nitrobenzene immobilized in the pores of a porous polypropylene hollow fiber, and into 30 μl of 10 mM HCOOH as acceptor solution inside the lumen of the hollow fiber. The driving force of the extraction was a 9 V potential sustained over the SLM with a common battery, with the positive electrode placed in the plasma sample and the negative electrode placed in the acceptor solution. Extractions were performed under totally stagnant conditions with a very simple device for 1 min (kinetic regime), and subsequently the acceptor solution was analyzed directly by liquid chromatography–mass spectrometry (LC–MS). Recoveries were 12, 13, 22, and 17% for fluoxetine, amitriptyline, citalopram, and fluvoxamine, respectively. Sample clean-up was comparable to reversed-phase solid-phase extraction (SPE), but EME required substantially less time than SPE. The time advantage of EME was further improved by parallel extraction of three samples (for 1 min) with the same 9 V battery. EME from plasma combined with LC–MS provided limits of quantification (S/N = 10) in the range 0.4–2.3 ng/ml, linearity in the range 1–1000 ng/ml with r2-values of 0.998–0.999, and repeatability in the range 3.2–8.9% RSD in the mid-therapeutic window (100 ng/ml). 相似文献
426.
With the implementation of recombinant DNA technology in the pharmaceutical industry, some synthetic insulins have been developed in order to improve the therapy of diabetes. These analogues differ only slightly in the amino acid sequence, therefore displaying a great challenge for analytical chemistry. Within the work presented in this paper, capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC) with sodium dodecylsulphate (SDS) as micelle-forming agent, and microemulsion electrokinetic chromatography (MEEKC) with microemulsions consisting of SDS, n-octane and 1-butanol were investigated for the separation of human insulin and five synthetic analogues. Best results were achieved with a solvent-modified MEKC system consisting of 100 mM sodium dodecyl sulphate and 15% acetonitrile in 10 mM borate buffer (pH 9.2). A similar system based on perfluorooctanoic acid as micelle-forming agent in ammonium acetate (pH 9.2) was successfully employed for the hyphenation with a quadrupole/time-of-flight mass spectrometer via a sheath-flow interface. In this case, detection limits at 10 mg/L could be achieved. 相似文献
427.
Berteloite C Lara M Bergeat A Le Picard SD Dayou F Hickson KM Canosa A Naulin C Launay JM Sims IR Costes M 《Physical review letters》2010,105(20):203201
We report combined studies on the prototypical S(1D2) + H2 insertion reaction. Kinetics and crossed-beam experiments are performed in experimental conditions approaching the cold energy regime, yielding absolute rate coefficients down to 5.8 K and relative integral cross sections to collision energies as low as 0.68 meV. They are supported by quantum calculations on a potential energy surface treating long-range interactions accurately. All results are consistent and the excitation function behavior is explained in terms of the cumulative contribution of various partial waves. 相似文献
428.
Vanessa Coremans Tariq Ahmed Detlef Balschun Rudi D'Hooge Astrid DeVriese Jonathan Cremer Flavia Antonucci Micha?l Moons Veerle Baekelandt Veerle Reumers Harold Cremer Amelia Eisch Diane Lagace Tom Janssens Yuri Bozzi Matteo Caleo Edward M Conway 《BMC neuroscience》2010,11(1):1-19
Background
Survivin is a unique member of the inhibitor of apoptosis protein (IAP) family in that it exhibits antiapoptotic properties and also promotes the cell cycle and mediates mitosis as a chromosome passenger protein. Survivin is highly expressed in neural precursor cells in the brain, yet its function there has not been elucidated.Results
To examine the role of neural precursor cell survivin, we first showed that survivin is normally expressed in periventricular neurogenic regions in the embryo, becoming restricted postnatally to proliferating and migrating NPCs in the key neurogenic sites, the subventricular zone (SVZ) and the subgranular zone (SGZ). We then used a conditional gene inactivation strategy to delete the survivin gene prenatally in those neurogenic regions. Lack of embryonic NPC survivin results in viable, fertile mice (Survivin Camcre ) with reduced numbers of SVZ NPCs, absent rostral migratory stream, and olfactory bulb hypoplasia. The phenotype can be partially rescued, as intracerebroventricular gene delivery of survivin during embryonic development increases olfactory bulb neurogenesis, detected postnatally. Survivin Camcre brains have fewer cortical inhibitory interneurons, contributing to enhanced sensitivity to seizures, and profound deficits in memory and learning.Conclusions
The findings highlight the critical role that survivin plays during neural development, deficiencies of which dramatically impact on postnatal neural function. 相似文献429.
In the stochastic multi-armed bandit problem we consider a modification of the UCB algorithm of Auer et al. [4]. For this modified algorithm we give an improved bound on the regret with respect to the optimal reward. While for the original UCB algorithm the regret in K-armed bandits after T trials is bounded by const · $ \frac{{K\log (T)}} {\Delta } $ , where Δ measures the distance between a suboptimal arm and the optimal arm, for the modified UCB algorithm we show an upper bound on the regret of const · $ \frac{{K\log (T\Delta ^2 )}} {\Delta } $ . 相似文献
430.
Crystal structure, thermochemical stability, transport and magnetic properties of compositions in the (100-x) La0.8Sr0.2MnO3 ± δ xCeO2 (LSMC) system were studied. All compositions in the LSMC series containing more than 2 mol% CeO2 were two phase and consisted of the modified perovskite constituent with rhombohedral structure (R3?c) and ceria as a secondary phase with cubic structure (Fm3?m). The presence of both Ce4+and Ce3+ cations in LSMC compositions was revealed by X-ray Photoelectron Spectroscopy (XPS). CeO2 and compositions in the LSMC series showed good thermochemical stability in air and argon. However, in H2–Ar atmosphere all LSMC compositions underwent reduction followed by decomposition. Transport and magnetic properties change in a non-linear way with the increase in the CeO2 content. The LSMC2 composition showed enhanced electronic conductivity and magnetic characteristics. Metallic type conductivity was observed for LSMC compositions with x ≤ 36 mol% CeO2 in a narrow temperature range of 770–900 °C. A small degree of substitution of Ce into LSM was found to change structural, magnetic and electrical properties. 相似文献