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排序方式: 共有219条查询结果,搜索用时 31 毫秒
1.
Cairns Grant; McIntyre Margaret; Ozdemir Mehmet 《Bulletin London Mathematical Society》1993,25(2):169-176
We prove that the number of vertices of a smooth normal planarcurve is at least 6, if it bounds a surface other than the disk. 相似文献
2.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献
3.
A current interpretation of XPS spectra of Ni metal assumes that the main 6 eV satellite is due to a two hole c3d94s2 (c is a core hole) final state effect. We report REELS observation in AES at low voltages of losses (plasmons and inter-band transitions) corresponding to the satellite structures in Ni metal 2p spectra. The satellite near 6 eV is attributed to a predominant surface plasmon loss. A current interpretation of Ni 2p spectra of oxides and other compounds is based on charge transfer assignments of the main peak at 854.6 eV and the broad satellite centred at around 861 eV to the cd9L and the unscreened cd8 final-state configurations, respectively (L is a ligand hole). Multiplet splittings have been shown to be necessary for assignment of Fe 2p and Cr 2p spectral profiles and chemical states. The assignments of Ni 2p states are re-examined with intra-atomic multiplet envelopes applied to Ni(OH)2, NiOOH and NiO spectra. It is shown that the free ion multiplet envelopes for Ni2+ and Ni3+ simulate the main line and satellite structures for Ni(OH)2 and NiOOH. Fitting the NiO Ni 2p spectral profile is not as straightforward as the hydroxide and oxyhydroxide. It may involve contributions from inter-atomic, non-local electronic coupling and screening effects with multiplet structures significantly different from the free ions as found for MnO. A scheme for fitting these spectra using multiplet envelopes is proposed. 相似文献
4.
Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe40Ni40B20 and Fe40Ni38Mo4B18 metallic glass ribbons. 90 MeV 127I beam was used for the irradiations. Irradiation doses were 5×1013 and 7.5×1013 ions/cm2. The relative intensity ratios D 23 of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy. 相似文献
5.
6.
H. Jara K. Boyer U. Johann T. S. Luk I. A. McIntyre A. McPherson C. K. Rhodes 《Applied physics. B, Lasers and optics》1987,42(1):11-15
The results of transient loss measurements performed in a self-sustained discharge KrF* amplifier are reported. Analysis of these results gives a minimum value of 20 for the effective gain to loss ratiog
0/eff, indicating that efficient extraction of energy in subpicosecond KrF* amplifiers in the 1 J range should be achievable. 相似文献
7.
Harrison KA Davies SS Marathe GK McIntyre T Prescott S Reddy KM Falck JR Murphy RC 《Journal of mass spectrometry : JMS》2000,35(2):224-236
Oxidized low-density lipoprotein (LDL) is thought to play an important role in atherogenesis and cardiovascular disease in humans. Oxidized LDL is a complex mixture of many oxidized species, including numerous oxidized glycerophospholipids. Electrospray ionization and tandem mass spectrometry as well as microchemical derivatization of high-performance liquid chromatographically purified fractions derived from oxidized LDL were investigated as means to determine the structure of individual components present in oxidized LDL. One major oxidized phosphocholine lipid had an [M + H](+) ion at m/z 650. Derivatization to the trimethylsilyl ether and methoxime caused shifts in mass which, along with negative ion collision-induced dissociation mass spectra, were consistent with the presence of three species, 1-palmitoyl-2-(9-oxononanoyl)glycerophosphocholine and two isomeric 1-octadecanoyl-2-(hydroxyheptenoyl)glycerophosphocholines. These species were chemically synthesized. Trimethylsilylation of free hydroxyl groups increased the mass of the phospholipid acyl chains containing hydroxyl groups by 72 u. Conversion of carbonyl groups to the methoxylamine derivative increased the mass by 29 u. Ozonolysis of those products which contained double bonds proved to be a facile technique to determine the position and number of double bonds present. The use of these techniques was illustrated in the structural characterization of one major component (m/z 650, positive ions) in oxidized LDL as 1-octadecanoyl-2-(7-hydroxyhepta-5-enoyl)glycerophosphocholi ne. A possible mechanism for the formation of this unique chain-shortened glycerophospholipid is proposed. 相似文献
8.
Renate Foerch N. S. McIntyre D. H. Hunter 《Journal of polymer science. Part A, Polymer chemistry》1990,28(1):193-204
The reaction rates and products of remote oxygen plasma treatment, corona discharge, and ozone treatment of high and low density polyethylenes have been examined using x-ray photoelectron spectroscopy. The oxygen uptake by remote plasma treatment was faster than that of other surface treatments using excited oxygen species. A steady state concentration of 18 ± 1% oxygen can be attained within 1 s of exposure in the remote plasma. 相似文献
9.
A single-crystal neutron diffraction analysis of the cluster complex [H(4)Co(4)(C(5)Me(4)Et)(4)] was carried out on the new quasi-Laue diffractometer VIVALDI at the Institut Laue-Langevin. The structure consists of four face-bridging hydrides attached to a tetrahedral cobalt metal core. Average distances and angles in the core of the molecule are as follows: Co-Co = 2.571(8), Co-C = 2.158(6), Co-H = 1.749(7), H.H = 2.366(9) A; Co-H-Co = 94.6(3), H-Co-H = 85.1(3) degrees. The hydride ligands are located off the Co-Co-Co planes by an average distance of 0.923(8) A. It is suggested that the dimensions of the HCo(3) fragments found in this molecule provide reasonable estimates for analogous distances and angles associated with chemisorbed H atoms situated on the 3-fold hollows of a cobalt surface. Crystallographic details: space group P2(1)/a (monoclinic); a = 21.979(2), b = 10.924(1), c = 34.406(2) A; beta = 90.81(1) degrees; Z = 8. Final agreement factor: R(F) = 0.099 for 3779 reflections [I > 2sigma(I)] collected at 20 K. 相似文献
10.
3-methylenebicyclo[2,2,1]heptane-2,6-carbolactone (previously incorrectly claimed) has now been prepared and converted to the 3-oxo-lactone. Some 3-hydroxy-bicyclo-[2,2,1]heptane-2,6-carbolactones have been prepared and their rates of oxidation with chromic acid determined. The results do not support a theory about the mechanism of oxidation, involving a dipolar interaction from the lactone. 相似文献