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171.
《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):831-835
e
+
e
- production was studied using the High Acceptance DiElectron Spectrometer (HADES). In pp collisions at 2.2GeV kinetic beam energy, the exclusive η production and the Dalitz decay η→γe
+
e
- have been reconstructed. The electromagnetic form factor of the latter decay was found to be in good agreement with the existing
theoretical predictions. In addition, an inclusive e
+
e
- invariant-mass spectrum from the 12C + 12C reaction at 2AGeV is presented and compared with a simplified thermal model. 相似文献
172.
Stress corrosion of silicate glass: a review 总被引:1,自引:0,他引:1
René Gy 《Journal of Non》2003,316(1):1-11
In the first section of the present paper, some examples, from the field, of the manifestations or consequences of the fatigue of silicate glass are briefly presented. In the second section, the interpretation of fatigue in terms of stress corrosion is reviewed: the role of ambient molecular water is well established. Whatever the details of the mechanism of action of water, it takes place very efficiently in the highly strained material close to the tip of a surface crack. This enables its sub-critical growth to be explained. But it does not explain many other observed effects of the environment on the mechanical behavior of silicate glass, and, in the last section, questions and issues are presented, which would still need to be investigated. 相似文献
173.
Vinod K. Tiwari Neetu Tewari Diksha Katiyar Rama P. Tripathi 《Monatshefte für Chemie / Chemical Monthly》2007,138(12):1297-1302
Summary. The one-pot reaction of β-glycosyl amino acids with β-ketoesters in the presence of Amberlite IR-120 resin and 4 ? molecular
sieve in refluxing toluene resulted in the respective dihydropyridones in fair to good yields.
Present address: Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi-221005, India. 相似文献
174.
Azevedo Lemos V Xavier Baliza PX Terumi Yamaki R Eça Rocha M Oliveira Alves AP 《Talanta》2003,61(5):675-682
An on-line system for preconcentration and determination of copper at μg l−1 level by flame atomic absorption spectrometry (FAAS) is proposed. Amberlite XAD-2 functionalized with 3,4-dihydroxybenzoic acid packed in a minicolumn was used as sorbent. Copper(II) ions were sorbed in the minicolumn, from which it could be eluted by hydrochloric acid solution directly to the nebulizer-burner system of the FAAS. Eluent solution was carried by water at a flow rate of 5.00 ml min−1. Signals were measured as peak height by using an instrument software. Achieved sampling rate was 27 samples per hour. Analytical parameters were evaluated and the results demonstrated that copper can be determined, with acetate buffer to adjust the sample pH at 6.0, preconcentration time of 120 s and a sample flow rate of 6.50 ml min−1. The desorption was carried out with 30 μl of a 1.0 mol l−1 hydrochloric acid solution. An enrichment factor of 33 in 13.00 ml of sample (120 s preconcentration time) was achieved by using the time-based technique. The detection limit (DL) (3 s) was 0.27 μg l−1 and the precision (assessed as the relative standard deviation) reached values of 5.7-1.1% in copper solutions of 5.00 to 50.00 μg l−1 concentration, respectively. The accuracy of procedure was confirmed by copper determination in certified reference materials. Recoveries of spike additions (1.0 or 2.0 μg g−1) to food samples were quantitative (90.0-110.0%). These results proved also that the procedure is not affected by matrix interference and can be applied satisfactorily for copper determination in rice flour and starch samples. 相似文献
175.
176.
Devdutt CHATURVEDI Nisha MISHRA Virendra MISHRA 《中国化学快报》2006,17(10):1309-1312
Organic carbamates exhibit unique physical, chemical and biological properties, accommodating variety of applications in pharmacology1 (drugs, prodrugs and drug intermediates), agriculture2 (pesticides, insecticides, fungicides, herbicides etc.) and as synthetic intermediates in chemical industry3. Their use as protection of amino groups in peptide synthesis4 and as linkers in combinatorial chemistry5 is also well known. Functionalization of amines as carbamates offers an attractive method for… 相似文献
177.
2-Hydroxybenzaldehyde-5-nitro-pyridylhydrazone (2HB-5NPH) was synthesized and its application in the spectrophotometric determination of metal ions was studied in the presence of surfactants. A separation procedure, using a short column filled with Amberlite IRC 718, is proposed for the spectrophotometric determination of traces of cobalt. The influence of several ions, as interference, was discussed. The procedure was applied to determination of cobalt in mixture sample with satisfactory results (≥recovery 96%; relative error ≤2%; relative standard deviation ≤1.2% in the concentration range of 0.02–2.0 mg l−1; detection limit, 0.01 mg l−1 in solution). Control of the pH during the column operation is essential because the adsorption capacities are very sensitive to change in pH. Their separation was carried out in 0.005 M Malic acid, 1.5 M HCl, 2.0 M HNO3 media. 相似文献
178.
David J. Green 《Journal of Non》2003,316(1):35-41
A new approach to chemical strengthening is to move the maximum residual compression below the glass surface. With appropriate processing, this approach leads to strengthening and a decrease in the strength variability. This improvement in mechanical reliability is accomplished by introducing stable crack growth into the glass, which leads to multiple cracking of the glass surface prior to failure. In the current study, a fracture mechanics analysis is presented that uses a simple form for the stress profile. By determining the effect of this stress profile on the apparent fracture toughness of the material, it is possible to identify the conditions when spontaneous cracking occurs, the stress for the onset of multiple cracking and the ultimate strength of the glass. In particular, it is shown there is an important interplay between the depth of the maximum compression, the stress gradient and the magnitude of the maximum compressive stress. The current analysis is then used to define a strategy for the processing of glasses with engineered stress profiles. 相似文献
179.
A stable chelating resin matrix was synthesized by covalently linking o-aminophenol (o-AP) with the benzene ring of the polystyrene–divinylbenzene resin, Amberlite XAD-2, through a –N=N– group. Elemental analyses, thermogravimetric analysis (TGA) and infrared spectra have characterized the resulting chelating resin. It has been used to preconcentrate Cu2+, Cd2+, Co2+, Ni2+, Zn2+ and Pb2+, prior to their determination by flame atomic absorption spectrometry. The optimum pH values for quantitative sorption of Cu, Cd, Co, Ni, Zn and Pb are 6.2–7.4, 5.6–7.2, 5.6–9.0, 6.0–9.0, 5.7–7.0 and 5.0–6.0, respectively. These metals are desorbed (recovery 91–98%) with 4 mol dm−3 HNO3. The sorption capacity of the resin is 3.37, 3.42, 3.29, 3.24, 2.94 and 3.32 mg of metal g−1 of resin, respectively, for Cu, Cd, Co, Ni, Zn and Pb. The effect of NaF, NaCl, NaNO3, Na2SO4, and Na3PO4 on the sorption of these metal ions has been investigated. These electrolytes are tolerable up to 0.01 mol dm−3 in case of all the metal ions, except Cl− which is tolerable even up to 0.1 mol dm−3 for Zn and 1.0 mol dm−3 for Pb. The preconcentration factor for Cu, Cd, Co, Ni, Zn and Pb are 50, 50, 100, 65, 40 and 40 (concentration level 10–25 μg dm−3) respectively. Simultaneous enrichment of the six metals is possible. The method has been applied to determine Cu, Cd, Co, Ni, Zn and Pb content in well water samples (RSD≤8%). 相似文献
180.
Valfredo Azevedo Lemos Ednilton Moreira Gama Adriana da Silva Lima 《Mikrochimica acta》2006,153(3-4):179-186
A new chelating sorbent has been developed using Amberlite XAD-2 resin anchored with pyrocatechol through the –CH2– group. This sorbent, characterised by elemental analysis and infrared (IR) spectra, was used as a packing material for a
minicolumn in an on-line preconcentration system for cadmium, cobalt and nickel determination. Metal ions were sorbed in the
minicolumn, from which it could be eluted directly to the nebulizer-burner system of the flame atomic absorption spectrometer
(FAAS). Metals can be eluted from the minicolumn with 0.50 mol L−1 HCl or HNO3. The enrichment factors were 22 (Cd), 23 (Co) and 25 (Ni), for 60 s preconcentration time, and 44 (Cd), 40 (Co) and 48 (Ni),
if 180 s preconcentration time was used. Under the optimum conditions, the procedure allowed the determination of cadmium,
cobalt and nickel with detection limits of 0.27, 0.59 and 1.29 μg L−1, respectively, when preconcentration periods of 180 s were used. The accuracy of the procedure was sufficient and evaluated
by analysing certified reference materials. The method was applied to the analysis of food samples (black tea and rice flour). 相似文献