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排序方式: 共有830条查询结果,搜索用时 15 毫秒
91.
We investigate the processes of cluster formation and growth of ZnS from aqueous solution using molecular dynamics simulation techniques. The influence of both temperature and concentration is studied. We show that, at lower temperatures, the crucial process is the transformation of an outer-sphere Zn/S complex to an inner-sphere ion pair. Further growth of the latter is fast to generate negatively charged planar clusters. These clusters interact to form more stable, closed structures, which are found to be the global minima configurations in vacuo. At higher temperatures, no outer-sphere ion pairs are formed, and the larger cluster configurations form much more quickly. 相似文献
92.
The salts [(C2H5)3NH]2[M4(SC6H5)10] (M = Zn, Cd) can be prepared by the electrochemical oxidation of the metal in an acetonitrile solution of triethylamine and benzenethiol. An X-ray crystal structure determination shows that the anion consists of a tetrahedron of metal atoms, each carrying a terminal -SC6H5 ligand, and connected to the three other metal atoms by bridging > SC6H5 groups. The results are compared with those for similar compounds reported in the literature. 相似文献
93.
94.
95.
Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene)
Verilhac JM Pokrop R LeBlevennec G Kulszewicz-Bajer I Buga K Zagorska M Sadki S Pron A 《The journal of physical chemistry. B》2006,110(27):13305-13309
Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight. 相似文献
96.
Hernán J. Cervantes Antonio C. Bloise Said R. Rabbani 《Applied magnetic resonance》2010,38(4):417-429
In this paper, we propose a new method of measuring the very slow paramagnetic ion diffusion coefficient using a commercial
high-resolution spectrometer. If there are distinct paramagnetic ions influencing the hydrogen nuclear magnetic relaxation
time differently, their diffusion coefficients can be measured separately. A cylindrical phantom filled with Fricke xylenol
gel solution and irradiated with gamma rays was used to validate the method. The Fricke xylenol gel solution was prepared
with 270 Bloom porcine gelatin, the phantom was irradiated with gamma rays originated from a 60Co source and a high-resolution 200 MHz nuclear magnetic resonance (NMR) spectrometer was used to obtain the phantom 1H profile in the presence of a linear magnetic field gradient. By observing the temporal evolution of the phantom NMR profile,
an apparent ferric ion diffusion coefficient of 0.50 μm2/ms due to ferric ions diffusion was obtained. In any medical process where the ionizing radiation is used, the dose planning
and the dose delivery are the key elements for the patient safety and success of treatment. These points become even more
important in modern conformal radio therapy techniques, such as stereotactic radiosurgery, where the delivered dose in a single
session of treatment can be an order of magnitude higher than the regular doses of radiotherapy. Several methods have been
proposed to obtain the three-dimensional (3-D) dose distribution. Recently, we proposed an alternative method for the 3-D
radiation dose mapping, where the ionizing radiation modifies the local relative concentration of Fe2+/Fe3+ in a phantom containing Fricke gel and this variation is associated to the MR image intensity. The smearing of the intensity
gradient is proportional to the diffusion coefficient of the Fe3+ and Fe2+ in the phantom. There are several methods for measurement of the ionic diffusion using NMR, however, they are applicable
when the diffusion is not very slow. 相似文献
97.
Said R. Grace John R. Graef Ercan Tunc 《Journal of Applied Analysis & Computation》2019,9(4):1305-1318
The authors present conditions under which every positive solution $x(t)$ of the integro--differential equation $x^{\prime \prime }(t)=a(t)+\int_{c}^{t}(t-s)^{\alpha-1}[e(s)+k(t,s)f(s,x(s))]ds, \quad c>1, \ \alpha >0,$ satisfies $x(t)=O(tA(t))\textrm{ as }t\rightarrow \infty,$ i.e, $\limsup_{t\rightarrow \infty }\frac{x(t)}{tA(t)}<\infty, \textrm{where} \ A(t)=\int_{c}^{t}a(s)ds.$ From the results obtained, they derive a technique that can be applied to some related integro--differential equations that are equivalent to certain fractional differential equations of Caputo type of any order. 相似文献
98.
An efficient method for preparation of 4,6 or 5,6 disubstituted 3-aminopyridazines was easily carried out starting from easily available 4-bromo-pyridazine-3,6-dione, and using combination of both amination and Pd(0) cross-coupling reactions under microwave irradiation. 相似文献
99.
In this work we consider a nonlinear hyperbolic one-dimensional viscoelastic nonlocal problem with a nonlocal boundary condition.
We establish a blow up result for large initial data and a decay result for small enough initial data. 相似文献
100.
Said Mesloub 《Mathematical Methods in the Applied Sciences》2010,33(1):57-70
In this paper, we study a nonlocal mixed problem for a nonlinear hyperbolic equation. Based on some a priori estimates and some density arguments, we prove the well posedness of the associated linear problem. The existence and uniqueness of the weak solution of the nonlinear problem are then established by applying an iterative process based on the obtained results for the linear problem. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献