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排序方式: 共有141条查询结果,搜索用时 31 毫秒
21.
MJ Singh DO Kataria N Madhavan P Sugathan JJ Das DK Awasthi AK Sinha R Shanker 《Pramana》1999,53(4):743-764
A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer
processes in collisions of 60–120 MeV Si
q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization,
electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated.
The data reported on the present collision system result from a direct measurement in the considered impact energy for the
first time. The total ionization cross-sections for the recoil ions are shown to scale as q
1.7/E
p
0.5
, where E
p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing
recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j
2 upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing
cross-sections σ
qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow
our data for different ionization processes is reviewed and discussed. 相似文献
22.
Surface spline interpolation when the domain is all of Rd isknown to converge much faster to the data function f than inthe case when the domain is the unit ball. This difference isunderstood to be due to boundary effects which, as will be shown,also affect the size of the surface spline's coefficients. Wepropose a modified form of surface spline interpolation which,to a great extent, overcomes these boundary effects. This modifiedsurface spline interpolant uses only the values of f at thegiven interpolation points. 相似文献
23.
24.
Burford N Conroy KD Landry JC Ragogna PJ Ferguson MJ McDonald R 《Inorganic chemistry》2004,43(26):8245-8251
Reactions of the cyclic diphosphadiazanes (XPNR)(2) (X = Cl, Br; R = 2,6-dimethylphenyl = Dmp, 2,6-diisopropylphenyl = Dipp) with GaX(3) followed by 4-(dimethylamino)pyridine (DMAP) give the corresponding trimers (XPNR)(3). An unusual cyclophosphazanium tetrachlorogallate salt [(DippN)(3)P(3)Cl(2)][GaCl(4)] has been isolated from the reaction of (ClPNDipp)(2) with GaCl(3) and represents an intermediate in the disproportionation process. Dissociation of the gallate ion on reaction of [(DippN)(3)P(3)Cl(2)][GaCl(4)] with DMAP releases a halide ion, which associates with the dicoordinate phosphenium center to give (ClPNDipp)(3). The observations indicate that the presence of medium-sized substituents at nitrogen (R) thermodynamically destabilize the dimer with respect to the trimer, without offering sufficient stabilization of the monomer, as observed for MesNPX (Mes* = 2,4,6-tri-tert-butylphenyl) (Mes* > Dipp > Dmp). Nevertheless, lability of the N-P bond in these derivatives of (XPNR)(2) allows for transformations between dimer and trimer that may include transient existence of the corresponding monomer. Manipulation of substituent steric strain to modify the relative stability of phosphazane oligomers provides a new methodology for diversification of phosphazane chemistry. 相似文献
25.
The quantitative separation by isothermal distillation of 50–100 ng of boron in 0.1 ml of sulfuric acid solution is possible in 10 min. if the sulfuric acid solution is made to react with 0.3 ml of methanol, and the trimethylboric ester formed is absorbed by 0.3 ml of sodium hydroxide solution at a concentration of 2 μg ml-1. Boron in the distilled fractions is measured by a fluorimetric method with HMCB. 相似文献
26.
Following the previous demonstration that low concentrations of inorganic sulfate (SO4) in human serum and cerebrospinal fluid can be accurately determined by controlled-flow anion chromatography, the assay has been extended to the quantitation of free SO4 in saliva and sweat by modification of the established methods of sample collection and preparation. Salivary secretions were ultrafiltered to remove macromolecular polyanions that bind irreversibly to the anion-exchange separator column and reduce resolution. Sweat was collected from 22 fasted adult volunteers using a method which utilizes absorbent filter pads applied to the forearm after secretion had been stimulated by pilocarpine iontophoresis. It was necessary to acid wash the filter pads to reduce sulfate contamination. Saliva ultrafiltrate or sweat was diluted and injected onto a Dionex D-10 Ion Analyzer using the standard anion column system. The mean inorganic SO4 concentration in saliva from seventeen adult fasting volunteers was 72 +/- 4 mumol/l (+/- S.E.); the mean SO4 concentration in sweat was 83 +/- 3 mumol/l. Both are significantly less than in matching serum, suggesting that SO4 is actively removed during formation of these glandular secretions. The ion chromatographic assay is shown to be capable of measuring SO4 in biological fluids at concentrations that are otherwise undetectable by conventional assay techniques. 相似文献
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