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1.
Ming Xia LI Yan Ming WANG Ru Ru CHEN* Research Institute of Elemento-Organic Chemistry Nankai University Tianjin Pittsburgh University Medical Center Pittsburgh PA U. S. A 《中国化学快报》2001,(6)
The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form… 相似文献
2.
We consider diffraction by a semi-infinite crack located alonga fusion interface between two differing elastic media. Twotypes of crack, namely open and partially closed cracks, areinvestigated. An open crack is modelled by a stress-free contactboundary condition and a partially closed crack is modelledby a spring contact boundary condition. For the latter, thejump in the stress across the crack is assumed to be proportionalto the jump in the displacement across the crack. This situationarises in, for example, a K-weld where the fine grain of theparent material (for example, ferritic or forged austeniticsteel) is in stark contrast with the coarse-grained weld metal(for example, austenitic weld metal). In the metal weld thedirection of the grain axis varies through the metal. However,diffraction is a local phenomenon and so the austenitic steelis assumed to have a zonal axis so that it may be modelled bya transversely isotropic composite. The ferritic or forged austeniticsteel will be modelled as an isotropic material. 相似文献
3.
Wijkens P Jastrzebski JT van Der Schaaf PA Kolly R Hafner A van Koten G 《Organic letters》2000,2(11):1621-1624
A general method for the functionalization of Si-Cl terminated carbosilane dendritic molecules via organolithium or organomagnesium reagents is described. Quantitative exchange of the bromine atoms of 4-bromophenyl-functionalized dendrimers affords polylithiated species that are valuable starting materials for further functionalization, e.g., into pyridyl alcohols. The latter were successfully applied as catalyst precursors in a ruthenium-mediated ring-closure metathesis reaction. 相似文献
4.
Green JS Ovchinnikov VM Evans RG Akli KU Azechi H Beg FN Bellei C Freeman RR Habara H Heathcote R Key MH King JA Lancaster KL Lopes NC Ma T MacKinnon AJ Markey K McPhee A Najmudin Z Nilson P Onofrei R Stephens R Takeda K Tanaka KA Theobald W Tanimoto T Waugh J Van Woerkom L Woolsey NC Zepf M Davies JR Norreys PA 《Physical review letters》2008,100(1):015003
Metal foil targets were irradiated with 1 mum wavelength (lambda) laser pulses of 5 ps duration and focused intensities (I) of up to 4x10;{19} W cm;{-2}, giving values of both Ilambda;{2} and pulse duration comparable to those required for fast ignition inertial fusion. The divergence of the electrons accelerated into the target was determined from spatially resolved measurements of x-ray K_{alpha} emission and from transverse probing of the plasma formed on the back of the foils. Comparison of the divergence with other published data shows that it increases with Ilambda;{2} and is independent of pulse duration. Two-dimensional particle-in-cell simulations reproduce these results, indicating that it is a fundamental property of the laser-plasma interaction. 相似文献
5.
Krushelnick K Rozmus W Wagner U Beg FN Bochkarev SG Clark EL Dangor AE Evans RG Gopal A Habara H Mangles SP Norreys PA Robinson AP Tatarakis M Wei MS Zepf M 《Physical review letters》2008,100(12):125005
Experiments were performed in which intense laser pulses (up to 9x10(19) W/cm(2)) were used to irradiate very thin (submicron) mass-limited aluminum foil targets. Such interactions generated high-order harmonic radiation (greater than the 25th order) which was detected at the rear of the target and which was significantly broadened, modulated, and depolarized because of passage through the dense relativistic plasma. The spectral modifications are shown to be due to the laser absorption into hot electrons and the subsequent sharply increasing relativistic electron component within the dense plasma. 相似文献
6.
A scheme for artificially collimating fast-electron beams produced in high intensity (>10(19) W cm(-2)) laser-solid interactions is proposed. The scheme uses a laser pulse at the relativistic threshold (approximately 10(18) W cm(-2)) that precedes the high intensity pulse to pregenerate a collimating magnetic field. This concept is supported by analytical calculations and numerical calculations performed using a novel hybrid-Vlasov-Fokker-Planck code called LEDA. This scheme may be highly useful for fast ignition inertial confinement fusion. 相似文献
7.
Willingale L Nilson PM Thomas AG Cobble J Craxton RS Maksimchuk A Norreys PA Sangster TC Scott RH Stoeckl C Zulick C Krushelnick K 《Physical review letters》2011,106(10):105002
Experiments were performed using the Omega EP laser, operating at 740 J of energy in 8 ps (90 TW), which provides extreme conditions relevant to fast ignition studies. A carbon and hydrogen plasma plume was used as the underdense target and the interaction of the laser pulse propagating and channeling through the plasma was imaged using proton radiography. The early time expansion, channel evolution, filamentation, and self-correction of the channel was measured on a single shot via this method. A channel wall modulation was observed and attributed to surface waves. After around 50 ps, the channel had evolved to show bubblelike structures, which may be due to postsoliton remnants. 相似文献
8.
Lundström E Brodin G Lundin J Marklund M Bingham R Collier J Mendonça JT Norreys P 《Physical review letters》2006,96(8):083602
The properties of four-wave interaction via the nonlinear quantum vacuum is investigated. The effect of the quantum vacuum is to generate photons with new frequencies and wave vectors, due to elastic photon-photon scattering. An expression for the number of generated photons is derived, and using state-of-the-art laser data it is found that the number of photons can reach detectable levels. In particular, the prospect of using the high-repetition Astra Gemini system at the Rutherford Appleton Laboratory is discussed. The problem of noise sources is reviewed, and it is found that the noise level can be reduced well below the signal level. Thus, detection of elastic photon-photon scattering may for the first time be achieved. 相似文献
9.
Zepf M Clark EL Beg FN Clarke RJ Dangor AE Gopal A Krushelnick K Norreys PA Tatarakis M Wagner U Wei MS 《Physical review letters》2003,90(6):064801
Measurements of energetic proton production resulting from the interaction of high-intensity laser pulses with foil targets are described. Through the use of layered foil targets and heating of the target material we are able to distinguish three distinct populations of protons. One high energy population is associated with a proton source near the front surface of the target and is observed to be emitted with a characteristic ring structure. A source of typically lower energy, lower divergence protons originates from the rear surface of the target. Finally, a qualitatively separate source of even lower energy protons and ions is observed with a large divergence. Acceleration mechanisms for these separate sources are discussed. 相似文献
10.
Gordeev SN Zhukov AA de Groot PA Jansen AG Gagnon R Taillefer L 《Physical review letters》2000,85(21):4594-4597
We report on transport measurements of YBa 2Cu 3O (7-delta) single crystals with different oxygen contents in the geometry B, J ||ab (J perpendicularB). Our data show that the vortices become confined between the Cu-O planes below a well-defined temperature at which the effective size 2xi of the vortex core is approximately equal to the period of the Cu-O layers. This confinement strongly increases the vortex liquid freezing temperature. A new melting line is found separating a vortex liquid and a smectic phase, which shows an oscillatory field dependence reflecting differences between commensurate and incommensurate smectic states. 相似文献