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691.
Spectra composed of hundreds of time components for absorption path lengths of up to 130 km have been recorded near 1050 nm by combination of two recent techniques, intracavity laser spectroscopy with vertical external cavity surface-emitting multiple-quantum-well lasers and time-resolved Fourier transform spectroscopy. A sensitivity of 1 x 10(-10) cm(-1) Hz(-1/2) is achieved for 10(4) simultaneously acquired spectral elements, 3 orders of magnitude better than the sensitivity obtained in previous similar experiments. Specific advantages of the method, especially for frequency and intensity metrology of weak absorption transitions, are discussed. 相似文献
692.
Traoré AS Godbout MJ Serre D Younan R Dionne G Dufour M Morin J Moisan C 《Magnetic resonance imaging》2003,21(6):609-615
The present study was undertaken to measure the gain observed in the liver-to-tumor contrast of perioperative images when using mangafodipir trisodium, a liver-specific contrast agent, during percutaneous cryosurgery of the liver performed under the guidance of magnetic resonance images. Retrospective quantitative analyses of MR images were performed on eleven patients having a total of 30 liver tumors treated by MR-guided percutaneous cryosurgery. An initial group of four patients were treated with no contrast agent, and was compared with a second group of 7 patients who received an intravenous injection of 5 microM/kg of mangafodipir for their cryosurgery. The percutaneous cryosurgery was monitored under the near-real-time-imaging mode of a 0.5T open-configuration MRI system using a T(1)-weighted Gradient-recalled echo pulse sequence. A significant improvement in the liver-to-tumor contrast-to-noise ratio was observed with mangafodipir (p < 0.05, paired t test) in 0.5T preoperative images. Along with the stability of the mangafodipir contrast enhancement during the entire cryosurgical procedure, the resulting gain in contrast allowed for better visualizing the presence of residual untreated tumor margins at the periphery of the cryosurgery iceball directly from perioperative images acquired with patients under narcosis. Consequently, it not only became easier for the interventionalist to determine the need for an additional cryoprobe to increase the size of the iceball during the procedure, but also to decide on the appropriate end point of the cryosurgery. 相似文献
693.
Carbene analogues of borazines are highly thermally stable. Keeping quasi-identical steric demands, the electronic properties of the carbene can be precisely tuned by varying the nature of the substituents at the boron centers. 相似文献
694.
Bar GL Lloyd-Jones GC Booker-Milburn KI 《Journal of the American Chemical Society》2005,127(20):7308-7309
A Pd(II) chloride precatalyst, in the presence of 1 equiv of benzoquinone, effects highly efficient, regioselective 1,2-diamination of 1,3-dienes using dialkyl ureas under mild conditions. There is no requirement for a large excess of diene. 相似文献
695.
Hydrodynamical modeling of heavy-ion collisions at RHIC suggests that the quark-gluon plasma (QGP) "thermalizes" in a remarkably short time scale, about 0.6 fm/c. We argue that this should be viewed as indicating fast isotropization, but not necessarily complete thermalization, of the nonequilibrium QGP. Non-Abelian plasma instabilities can drive local isotropization of an anisotropic QGP on a time scale which is faster than ordinary perturbative scattering processes. As a result, we argue that theoretical expectations based on weak-coupling analysis are not necessarily in conflict with hydrodynamic modeling of the early part of RHIC collisions, provided one recognizes the key role of non-Abelian plasma instabilities. 相似文献
696.
Using homogenization theory, we derive the effective permittivity and permeability of a wire-mesh photonic crystal from first principles. We show that this structure does not lead to a left-handed medium when it is embedded in a matrix with a negative mu, but that resonators in a medium with a negative epsilon do form a left-handed medium in the correct range of frequencies. 相似文献
697.
Guy Jumarie 《Central European Journal of Physics》2008,6(3):737-753
In a first stage, the paper deals with the derivation and the solution of the equation of the probability density function
of a stochastic system driven simultaneously by a fractional Gaussian white noise and a fractional Poissonian white noise
both of the same order. The key is the Taylor’s series of fractional order f(x + h) = E
α(hαD
x
α)f(x) where E
α() denotes the Mittag-Leffler function, and D
x
α is the so-called modified Riemann-Liouville fractional derivative which removes the effects of the non-zero initial value
of the function under consideration. The corresponding fractional linear partial differential equation is solved by using
a suitable extension of the Lagrange’s technique involving an auxiliary set of fractional differential equations. As an example,
one considers a half-oscillator of fractional order driven by a fractional Poissonian noise.
相似文献
698.
The electric response of several isolated rat hearts in a controlled environment was studied experimentally. The correlation dimension D(2) was estimated and was found to be between 4 and 6.5 when the response was nearly periodic. The variation of D(2) with the concentration of calcium was studied and a general trend of its increase with increasing concentration was found. Two types of ventricular fibrillation (VF) were observed, one that corresponds to a stochastic signal where D(2) is unbounded and the other to a low dimensional dynamical system with 3.5=D(2)=4. It was found also that for the heart the correlation dimension is only an approximate concept. A new method for the estimation of D(2), that is suitable for the case when it is only approximate was introduced. A surrogate data method suitable for the analysis of nearly periodic series was implemented. (c) 2000 American Institute of Physics. 相似文献
699.
Guy Mayer 《Optics Communications》1979,31(3):388-392
Fresnel and Fizeau have shown that the refraction index of matter depends on its velocity. We discuss the eventuality of a corresponding reverse effect: a travelling wave may induce momentum changes in transparent matter. 相似文献
700.
The technique of instrumental neutron activation analysis, involving neutron fluxes of 1014 n·cm−2·sec−1 and high resolution Ge(Li) gamma-detectors, has been applied to the analysis of bullet lead and jacket material. Radiochemical
separation of the majority of the radioantimony from the irradiated bullet material was performed, with the objective of facilitating
measurement of other elements present. Eight elements were measured in bullet lead and four in jacket material. Concentration
variations between the varieties of ammunition studied indicate that more extensive studies, directed to possible ammunition
characterisation, would be worthwhile. 相似文献