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81.
Vogt U Lindblom M Jansson PA Tuohimaa TT Holmberg A Hertz HM Wieland M Wilhein T 《Optics letters》2005,30(16):2167-2169
We report on a compact interferometer for the water-window soft-x-ray range that is suitable for operation with laser-plasma sources. The interferometer consists of a single diffractive optical element that focuses impinging x rays to two focal spots. The light from these two secondary sources forms the interference pattern. The interferometer was operated with a liquid-nitrogen jet laser-plasma source at lambda=2.88 nm. Scalar wave-field propagation was used to simulate the interference pattern, showing good correspondence between theoretical and experimental results. The diffractive optical element can simultaneously be used as an imaging optic, and we demonstrate soft-x-ray microscopy with interferometric contrast enhancement of a phase object. 相似文献
82.
Busacca CA Grossbach D Campbell SJ Dong Y Eriksson MC Harris RE Jones PJ Kim JY Lorenz JC McKellop KB O'Brien EM Qiu F Simpson RD Smith L So RC Spinelli EM Vitous J Zavattaro C 《The Journal of organic chemistry》2004,69(16):5187-5195
The Boehringer-Ingelheim phosphinoimidazoline (BIPI) ligands were applied to the formation of chiral quaternary centers in the asymmetric Heck reaction. Several different substrates were examined in detail, using more than 70 members of this new ligand class. Hammett relationships were determined through systematic variation of the ligand electronics. All substrates showed essentially the same Hammett behavior, where enantioselectivity increased as the ligands were made more electron-deficient. Ligand optimization has led to catalysts which give the highest enantioselectivities reported to date for these difficult systems. 相似文献
83.
Buser M Frommhold L Gustafsson M Moraldi M Champagne MH Hunt KL 《The Journal of chemical physics》2004,121(6):2617-2621
Quantum line shape calculations of the rototranslational enhancement spectra of nitrogen-methane gaseous mixtures are reported. The calculations are based on a recent theoretical dipole function for interacting N(2) and CH(4) molecules, which accounts for the long-range induction mechanisms: multipolar inductions and dispersion force-induced dipoles. Multipolar induction alone was often found to approximate the actual dipole surfaces of pairs of interacting linear molecules reasonably well. However, in the case of the N(2)-CH(4) pair, the absorption spectra calculated with such a dipole function still show a substantial intensity defect at the high frequencies (>250 cm(-1)) when compared to existing measurements at temperatures from 126 to 297 K, much as was previously reported. 相似文献
84.
Nilsson SL Bylund D Jörntén-Karlsson M Petersson P Markides KE 《Electrophoresis》2004,25(13):2100-2107
A chemometrics approach has been used for evaluating the effect of four experimental parameters when coupling capillary electrophoresis (CE) to electrospray ionization-mass spectrometry (ESI-MS). Electrospray voltage, sheath-liquid flow rate, nebulizing gas flow rate, and spray needle position in respect to the MS orifice were varied according to a full factorial design. In addition to main effects, two interaction effects could be identified as significant when measuring the peak intensity of the analytes, from a sample mixture containing peptides and pharmaceuticals. The first interaction effects, between the nebulizing gas flow rate and the sheath-liquid flow rate, and the second interaction effect, between the nebulizing gas flow rate and the spray position, could further explain the impact that these variables have on the spray performance. The number of theoretical plates and the baseline noise were also measured. The sheath-liquid flow was found to significantly affect the separation efficiency, while the noise level mainly was controlled by the nebulizing gas flow. The same factorial design was also used for a CE capillary with lower internal diameter (ID) and the effects of the same variables were compared on those capillaries using equal injection volume for both capillaries. Similar trends were obtained in both capillaries but capillary ID was shown to be a significant variable when evaluating both capillaries in a single model. It was found that a capillary with 25 microm ID provided improved CE-MS performance over than corresponding 50 microm ID capillary. Enhanced sensitivity was obtained using the narrow-bore capillary, and at lower sheath-liquid flow rate the 25 microm ID capillary also gave rise to more efficient peaks. 相似文献
85.
Van Parijs SM Corkeron PJ Harvey J Hayes SA Mellinger DK Rouget PA Thompson PM Wahlberg M Kovacs KM 《The Journal of the Acoustical Society of America》2003,113(6):3403-3410
Comparative analyses of the roar vocalization of male harbor seals from ten sites throughout their distribution showed that vocal variation occurs at the oceanic, regional, population, and subpopulation level. Genetic barriers based on the physical distance between harbor seal populations present a likely explanation for some of the observed vocal variation. However, site-specific vocal variations were present between genetically mixed subpopulations in California. A tree-based classification analysis grouped Scottish populations together with eastern Pacific sites, rather than amongst Atlantic sites as would be expected if variation was based purely on genetics. Lastly, within the classification tree no individual vocal parameter was consistently responsible for consecutive splits between geographic sites. Combined, these factors suggest that site-specific variation influences the development of vocal structure in harbor seals and these factors may provide evidence for the occurrence of vocal dialects. 相似文献
86.
Hagslätt H Jönsson B Nydén M Söderman O 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2003,161(2):138-147
Pulsed field gradient NMR diffusometry is a promising tool for investigating structures of porous material through determinations of dynamic displacements of molecules in porous systems. A problem with this approach is the lack of closed analytical expressions for echo-decays in anything but idealized pore geometries. We present here an approach based on calculating the appropriate diffusion propagator by means of finite element calculations. The suggested method is quite general, and can be applied to arbitrary porous systems. The protocol for the calculations is outlined and we show results from some different cases: diffusion in confined geometries and in systems that are spatially inhomogeneous with respect to concentration. 相似文献
87.
88.
Evans DA Seidel D Rueping M Lam HW Shaw JT Downey CW 《Journal of the American Chemical Society》2003,125(42):12692-12693
A highly enantioselective, nitroaldol reaction catalyzed by a chiral Cu(II) bis(oxazoline) complex has been developed. The reaction scope includes both aromatic and aliphatic aldehydes (15 examples) affording products in good yields and enantioselectivities (87-94% ee). An X-ray structure of the catalyst has been provided along with a rationalization of the sense of asymmetric induction. 相似文献
89.
We derive exact expressions for a number of aging functions that are scaling limits of nonequilibrium correlations, R(t(w),t(w)+t) as t(w)-->infinity, t/t(w)-->theta, in the 1D homogenous q-state Potts model for all q with T = 0 dynamics following a quench from T = infinity. One such quantity is (0)(t(w));sigma-->(n)(t(w)+t)> when n/square root of ([t(w))-->z. Exact, closed-form expressions are also obtained when an interlude of T = infinity dynamics occurs. Our derivations express the scaling limit via coalescing Brownian paths and a "Brownian space-time spanning tree," which also yields other aging functions, such as the persistence probability of no spin flip at 0 between t(w) and t(w)+t. 相似文献
90.
We demonstrate a simple low-voltage technique for gating the flow of aqueous liquids in microfluidic systems employing the electrochemically-controlled surface energy of the conjugated polymer poly(3-hexylthiophene). 相似文献