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321.
322.
The 532 or 355 nm laser-induced photoisomerization of allylic alcohols to aldehydes catalyzed by [Fe(3)(CO)(12)] or [Fe(CO)(4)PPh(3)] in hexane was investigated. The Fourier transform infrared (FTIR) absorption spectra of iron-carbonyl intermediate species such as [Fe(CO)(5)], [Fe(CO)(4)(R-C(3)H(4)OH)], and more importantly the pi-allyl iron-carbonyl hydride species [FeH(CO)(3)(R-C(3)H(3)OH)] (R=H, Me, Ph) were recorded during the catalytic process using [Fe(3)(CO)(12)] as the catalytic precursor. When [Fe(CO)(4)PPh(3)] was photolyzed with 355 nm, [FeH(CO)(3)(R-C(3)H(3)OH)] was also generated indicating the common occurrence of the species in these two systems. The pi-allyl hydride species is long believed to be a key intermediates and its detection here lends support to the pi-allyl mechanism of the photoisomerization of allyl alcohols. 相似文献
323.
The effect of power ultrasound application on DC hollow needle to plate atmospheric pressure electrical discharge enhanced by the flow of air through the needle electrode was studied experimentally. It was found that applying ultrasound increases discharge volume. In this volume take place plasmachemical processes, used in important ecological applications such as the production of ozone, VOC decomposition and de-NOx processes enhancement. In our experiments we used a negatively biased needle electrode as a cathode and a perpendicularly placed surface of the ultrasonic resonator--horn--as an anode. To demonstrate the effect of ultrasound waves on electrical discharge photographs of the discharge for the needle to the ultrasonic resonator at distances of 4, 6 and 8mm are shown. By varying the distance between needle and the surface of the transducer, we were able to create the node or the antinode at the region around the tip of the needle, where the ionization processes are effective. In our experimental arrangement the amplitude of acoustic pressure at antinode exceeded 10(4) Pa. The photographs reveal that the diameter of the discharge on the surface of the ultrasonic horn is increased when ultrasound is applied. The increase of discharge volume caused by the application of ultrasound can be explained as a combined effect of the change of the reduced electric field E/n (E is electric field strength and n is the neutral particles density), strong turbulence of the particles in the discharge region caused by quick changes of amplitudes of the standing ultrasonic wave and finally by the boundary layer near the ultrasonic transducer perturbations due to vibrations of the transducer surface. 相似文献
324.
Neuronal currents produce weak transient magnetic fields, and the hypothesis being investigated here is that the components of these parallel to the B0 field can potentially modulate the MR signal, thus providing a means of direct detection of nerve impulses. A theory for the phase and amplitude changes of the MR signal over time due to an external magnetic field has been developed to predict this modulation. Experimentally, a fast gradient-echo EPI sequence (TR = 158 ms, TE = 32.4 ms) was employed in an attempt to directly detect these neuronal currents in the adult human optic nerve and visual cortex using a 280-mm quadrature head coil at 1.5 T. A symmetrical intravoxel field distribution, which can be plausibly hypothesized for the axonal fields in the optic nerve and visual cortex, would result in phase cancellation within a voxel, and hence, only amplitude changes would be expected. On the other hand, an asymmetrical intravoxel field distribution would produce both phase and amplitude changes. The in vivo magnitude image data sets show a significant nerve firing detection rate of 56%, with zero detection using the phase image data sets. The percentage magnitude signal changes relative to the fully relaxed equilibrium signal fall within a predicted RMS field range of 1.2-2.1 nT in the optic nerve and 0.4-0.6 nT in the visual cortex, according to the hypothesis that the axonal fields create a symmetrical Lorentzian field distribution within the voxel. 相似文献
325.
An-Chi Wei Jyh-Rou Sze Jyh-Long Chern 《Applied Physics A: Materials Science & Processing》2010,101(2):411-416
The proposed optical systems are designed for extending the depths of foci (DOF) of UV lasers, which can be exploited in the
laser-ablation technologies, such as laser machining and lithography. The designed systems are commonly constructed by an
optical module that has at least one aspherical surface. Two configurations of optical module, lens-only and lens-reflector,
are presented with the designs of 2-lens and 1-lens-1-reflector demonstrated by commercially optical software. Compared with
conventional DOF-enhanced systems, which required the chromatic aberration lenses and the light sources with multiple wavelengths,
the proposed designs are adapted to the single-wavelength systems, leading to more economical and efficient systems. 相似文献
326.
We show here that metallic impurities presented in graphenes prepared from graphite can be usefully employed for electroanalysis. We demonstrate that cumene hydroperoxide electrochemical reduction on graphene containing iron-based impurities provides significantly larger voltammetric currents than the same experiment using iron oxide nanoparticles. This opens doors for turning metallic impurities into potentially useful components of graphene based electrochemical systems. 相似文献
327.
Changes in the wavelength expressed by the wave potential (the product of wavelength and the longitudinal electric field intensity) are investigated in the dependence on (similarity) parameters of the neon and argon d.c. discharge. The measured dependences show the influence of different state of the electron gas, which behaves hydrodynamically or kinetically (with spatial resonances) in dependence on the type of prevailing energy exchange by elastic, inelastic or Coulomb collisions. 相似文献
328.
Atomic fluorine has been lased at pressures up to 30 psia in a double discharge laser with vigorous flashboard pre-ionization. The spectral output of the laser is a function of pressure, with low pressure favoring doublet transitions and high pressure inducing new laser transitions in the quartet manifold. 相似文献
329.
Michael Nee Yu Chun Michael E. Squillacote John D. Roberts 《Magnetic resonance in chemistry : MRC》1982,18(3):125-127
The base-catalyzed ? NH2 exchange reactions of acetamide and thioacetamide were studied by 15N nuclear magnetic resonance spectroscopy by the use of line-shape analysis. The 15N NMR spectra of these primary amides at intermediate exchange rates were broad doublets, which indicated that the two amide protons were exchanging at different rates. The line-shape analysis indicated that the ratio of exchange rates was 6±1 for acetamide and 3±1 for thioacetamide. 相似文献
330.