首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
3.
4.
The 31P{1H} nuclear Overhauser effects (NOE's) and 31P-spin-lattice relaxation times (T1) for a series of trans-[PdCl2P2], P ? PEt3, PPr3n, PBu3n, PMe2Ph, PMePh2, P(p-Tol)3, P(cyclohexyl)3 complexes are reported. Both the NOE and T1 values depend upon the choice of solvent. The dipole-dipole mechanism dominates the spin-lattice relaxation of the coordinated phosphorus atom with the T1 values for the PEt3, PPr3n, and P (cyclohexyl)3 complexes decreasing with increasing molecular weight of the phosphine.  相似文献   

5.
6.
7.
The spin-lattice relaxation time (T 1) of 23 Na was measured in solutions of NaClO 4 and (or) NaBr in formamide,N-methylformamide,N,N-dimethylformamide (DMF), MeCN, Me2CO, tetrahydrofuran (THF), and dimethyl sulfoxide (DMSO), and 133 Cs in a solution of CsCl in formamide. The values of (1/T 1) 0 obtained by extrapolation are discussed in terms of current theories of quadrupolar magnetic relaxation of ionic nuclei. A correlation was found between (1/T 1) 0 for 23 Na and Gutmann's donor numbers.For Part I, see ref. 1.  相似文献   

8.
9.
10.
Summary An empirical method of extrapolating and interpolating gas chromatographic retention times obtained at three equally spaced isothermal temperatures is described. The accuracy of the method was evaluated from retention time data obtained using packed glass columns. A procedure for constructing retention time tables for homologous series and the derivation of an equation for calculating retention times as a function of temperature is also presented.  相似文献   

11.
12.
A relation between the correlation times τP and τJ for a system of hard spheres of arbitrary roughness has been found in the uncorr  相似文献   

13.
Using isocratic retention parameters, the gradient elution retention time for several proteins has been calculated. The gradient retention time calculation is based on fitting the isocratic retention data to an equation of the form: log k' = m log (1/[Ca2+]) + log K and on applying well-established principles of gradient elution. A good correlation between the observed and calculated retention times for several test proteins was obtained at various total gradient times and column flow-rates. Conversely, isocratic retention parameters characterizing protein retention can be calculated from gradient elution retention data. However, even with retention data of high quality, small errors are amplified by the log-log nature of the ion-exchange isocratic retention model employed. Based on the close correlation between predicted and observed gradient retention times, no evidence for protein denaturation resulting from immobilization of the protein at high initial k' values at or near the column inlet was observed.  相似文献   

14.
An acoustic waveguide device was shown to be sensitive to the molecular weight of poly(ethylene glycol) in solution over a molecular weight range determined by the operating frequency of the device. The acoustic device used generates a shear wave with displacement in the plane of the device surface and normal to the direction of propagation. Liquid over the device exhibits viscous coupling to the oscillating surface, affecting propagation of the acoustic wave. The propagation loss was shown to be directly proportional to the weight percentage of the solute. For a given weight percent of polymer in solution, the loss increased with increasing molecular weight until a maximum loss value was reached; this may be due to the fact that rotational times for polymer molecules increase with molecular weight until they reach a point at which the rotation is limited by the oscillation time on the device surface. The molecular weight at which the maximum loss value was attained was 10,000 g/mol for a device operating at 104 MHz and 3350 g/mol for a device operating at 331 MHz, implying a rotational time of 1 ns for each 2200 increase in molecular weight. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1490–1495, 2002  相似文献   

15.
A semi-empirical formula for orientational relaxation times of worm-like chains in dilute solutions is proposed where τrod = τ0N3 is the relaxation time of a rigid rod composed of N segments, and x = 2a/L is the chain rigidity, i.e. the ratio of the double persistence length to the chain contour length, L. The formula, which can be used in the entire range of molecular rigidities and chain lengths, has been tested against segment relaxation times for semi-rigid chains calculated from the optimized Rouse-Zimm model.  相似文献   

16.
Recovery times for the photobleaching of the saturable absorbing dye DODCI by picosecond pulse excitation are reported. Variations in DODCI concentration and exciting pulse power density result in recovery times ranging from ≈10 ps at high concentration/high power to >250 ps at low concentration/low power. These results not only corroborate out earlier data for fast recovery times in DODCI but also explain the inability of other investigations to confirm these findings.  相似文献   

17.
The concentrations of89Sr,90Sr,210Pb and210Po were measured in a series of rain samples collected at Fayetteville (36°N, 94°W), Arkansas, after the 14th Chinese test of March 18, 1972, which occurred at Lop Nor (40°N, 90°E), China. Approximately concordant tropospheric residence times were obtained from the89Sr/90Sr and210Po/210Pb ratios in rain. The89Sr/90Sr ratios were also measured for the rain samples collected at Tokyo (36°N, 140°E), Japan, and at Ankara (40°N, 33°E), Turkey.  相似文献   

18.
19.
The equilibrium residence times of the nonionic surfactant nonylphenol ethoxylate (NP100) in a latex dispersion were determined using NMR diffusometry. At 16% w/w particle concentration and 0.12, 0.43 and 0.81% w/w NP100, the residence times of the surfactant were 0.16, 1.02 and 4.73 s in solution (tau(A)) and 0.3, 0.37 and 0.61 s on the surface of the particles (tau(B)), respectively. At even higher particle concentration (>45% w/w), tau(A) and tau(B) were 1.47 and 2.2 s. Calculating the number of collisions that ought to result in adsorbed species, at 16% w/w, only 2, 5 and 2 per thousand (corresponding to 0.12, 0.43 and 0.81% w/w NP100) resulted in adsorption, whereas at >45% w/w, only 12 per thousand resulted in adsorption, which suggested that the surfactant was irreversibly adsorbed on the particles. The small increase in collision frequency with increased particle concentration could be a result of a diffusion controlled adsorption, while an energy barrier for desorption controlled the overall exchange dynamics in the dispersion. The slow dynamics in the dispersion was controlled, mainly by the nonylphenol group, which gave NP100 a strong preference to surfaces. In addition, the chain length of the poly(ethylene glycol) (PEG) group changed the solution behavior from being that of a typical surfactant to that of a polymer.  相似文献   

20.
Response times and voltages for PDLC light shutters   总被引:1,自引:0,他引:1  
The response times and operating voltages of light shutters formed from polymer dispersed liquid crystals (PDLCs) have been studied experimentally and the results compared with calculations based on non-sperhically shaped nematic droplet models. The experiments were performed on light shutters with elongated and uniformly aligned droplets where the relaxation time and voltage response were measured. It is shown that the droplet shape can be a dominant factor, particularly for the relaxation time, and the data are compared with equations derived in terms of the aspect ratio of the droplet l = a/b, where a and b are the lengths of the semi-major and semi-minor axes, respectively, of the elongated droplet. It is further demonstrated that the electric field inside the droplet can be considerably smaller than the applied field, due to the conductivity and dielectric properties of the polymer and liquid crystal materials. These data are used to obtain values for the ratio of the conductivities of the polymer binder and liquid crystal droplet, as well as the anisotropy of the conductivity in the liquid crystal.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号