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排序方式: 共有126条查询结果,搜索用时 15 毫秒
31.
Poly(methyloctylsiloxane) (PMOS) was sorbed into the pores of HPLC silica by a solvent evaporation procedure, then irradiated with gamma rays from a cobalt-60 source to absorbed doses in the range from 0 to 200 kGy (1Gy = 1J kg-1). Non-irradiated and irradiated samples were characterized by solvent extraction, specific surface area determination, infrared spectroscopy and reversed-phase column performance. Solvent extraction data reveal that about 40% of the PMOS is not extractable prior to irradiation and this increases to about 75% with radiation doses of 50 kGy or higher. Column performance was improved by the radiation treatment, reaching a maximum efficiency in the dose range of 80-140 kGy while the peak symmetry changed from As = 1.7 to 1.1. The improvement is attributed to the increased mass of polymer immobilized by the radiation treatment and to a more uniform distribution of the immobilized polymer in the silica pore system. A multi-layer stationary-phase model is presented in which the first layer consists of an adsorbed monolayer of PMOS and the second layer is immobilized by gamma radiation. 相似文献
32.
Marcos Jardim 《代数通讯》2013,41(1):288-298
We show that instanton bundles of rank r ≤ 2n ? 1, defined as the cohomology of certain linear monads, on an n-dimensional projective variety with cyclic Picard group are semistable in the sense of Mumford–Takemoto. Furthermore, we show that rank r ≤ n linear bundles with nonzero first Chern class over such varieties are stable. We also show that these bounds are sharp. 相似文献
33.
Manuel E. Rodrigues Deborah F. Jardim Stéphane J. M. Houndjo Ratbay Myrzakulov 《General Relativity and Gravitation》2013,45(11):2309-2323
We obtain a new phantom black plane solution in $4$ 4 D of the Einstein–Maxwell theory coupled with a cosmological constant. We analyse their basic properties, as well as its causal structure, and obtain the extensive and intensive thermodynamic variables, as well as the specific heat and the first law. Through the specific heat and the so-called geometric methods, we analyse in detail their thermodynamic properties, the extreme and phase transition limits, as well as the local and global stabilities of the system. The normal case is shown with an extreme limit and the phantom one with a phase transition only for null mass, which is physically inaccessible. The systems present local and global stabilities for certain values of the entropy density with respect to the electric charge, for the canonical and grand canonical ensembles. 相似文献
34.
35.
New monofunctional C18 urea stationary phases with sterically protecting dimethyl and diisopropyl groups were prepared by a single step modification process. ProntoSil spherical silica (3 microm) was chemically modified with the monofunctional ethoxysilanes, [(3-octadecylurea)propyl]dimethyl and [(3-octadecylurea)propyl]diisopropyl ethoxysilanes. The phases were characterized by elemental analysis, infrared and solid-state 29Si and 13C NMR spectroscopies. Chromatographic characterizations of the new phases in 50x3.9 mm HPLC columns were performed by the separation of two different test mixtures, containing nonpolar, polar and highly basic compounds. 相似文献
36.
Polese L Minelli EV Jardim EF Ribeiro ML 《Analytical and bioanalytical chemistry》1996,354(4):474-476
A small-scale method was developed for the simultaneous determination of gamma-HCH, heptachlor, aldrin, dicofol, mirex, endosulfan I, endosulfan II and endosulfan sulphate in soil. The extraction and clean-up steps were combined into one step by transferring soil samples to chromatographic columns prepacked with neutral alumina. The pesticides elution was processed with n-hexane : dichloromethane (7 : 3) and the concentrated eluate was analysed using gas-liquid chromatography with electron capture detection. Analyses of the "in vitro" fortified samples with the selected pesticides were performed at three different levels. Mean recoveries for aldrin, gamma-HCH and heptachlor, at levels of 2, 10 and 20 ng/g, ranged from 71 to 87%; for dicofol, at levels of 8, 40 and 80 ng/g, ranged from 97 to 103%; for endosulfan I and II, at levels of 5, 25 and 50 ng/g, ranged from 88 to 96%; for mirex, at levels of 6, 30 and 60 ng/g, ranged from 86 to 110%; and for endosulfan sulphate, at levels of 15, 75 and 150 ng/g, ranged from 93 to 104%. The method can be used for rapid determination of these pesticides in soil. 相似文献
37.
38.
E. Govea-Alcaide I. García-Fornaris P. Muné R. F. Jardim 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(4):373-378
Measurements of the electrical resistivity as a function
of temperature, ρ(T), for different values of applied
magnetic field, Ba (0 ≤ Ba ≤ 50 mT), were performed in
polycrystalline samples of Bi1.65Pb0.35Sr2Ca2
Cu3O10+δ subjected to different uniaxial compacting
pressure (UCP). We have found appreciable differences in the grain
orientation between samples by using X-ray diffractometry. From
the X-ray diffraction patterns performed, in powder and pellet
samples, we have estimated the Lotgering factor along the (00l)
direction, F(00l). The results indicate that F(00l)
increases ~23% with increasing UCP suggesting that grains
of these samples are preferentially aligned along the c-axis,
which is parallel to the compacting direction. The resistive
transition of the samples have been interpreted in terms of the
thermally activated flux-creep model. In addition, the effective
intergranular pinning energy, U0, have been determined for
different applied magnetic field. The magnetic field dependence of
U0, for Ba > 8 mT, was found to follow a H- α
dependence with α = 0.5 for all samples. The analysis of the
experimental data strongly suggested that increasing UCP results
in appreciable changes in both the grain alignment and the grain
connectivity of the samples. We have successfully interpreted the
data by considering the existence of three different
superconducting levels within the samples: the superconducting
grains, the weak-links, and the superconducting clusters. 相似文献
39.
40.
Celliers PM Collins GW Da Silva LB Gold DM Cauble R Wallace RJ Foord ME Hammel BA 《Physical review letters》2000,84(24):5564-5567
Simultaneous measurements of shock velocity and optical reflectance at 1064, 808, and 404 nm of a high pressure shock front propagating through liquid deuterium show a continuous increase in reflectance from below 10% and saturating at approximately (40-60)% in the range of shock velocities from 12 to 20 &mgr;m/ns (pressure range 17-50 GPa). The high optical reflectance is evidence that the shocked deuterium reaches a conducting state characteristic of a metallic fluid. Above 20 &mgr;m/ns shock velocity (50 GPa pressure) reflectance is constant indicating that the transformation is substantially complete. 相似文献