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181.
Esthy Levy Dehong Yu Yitzhak Mastai R.C. Ford 《Journal of solid state chemistry》2010,183(7):1691-1696
A series of quasi-elastic neutron scattering measurements were performed using IN6 at the Institute Laue Langevin for a mesoporous organosilica material with phenyl functions, called phenyltriethoxysilane (PTES). The aim of the experiment was to study the diffusion dynamics of nano-scale water clusters inside the hydrophobic pores as a function of temperature and hydration. By fitting the Debye-Waller factor, the data show clearly the different behavior between water, both inside and outside the hydrophobic pores, which resembles bulk water. The mean thermal displacement 〈u2〉 of the external water increases with T almost linearly up to 353 K, while the internal water quickly reaches the maximum at T∼323 K, indicating the confinement by an averaged pore diameter of the porous organosilica. 相似文献
182.
N.M. Blagoveshchenskii A.G. Novikov V.V. Savostin 《Physica B: Condensed Matter》2012,407(23):4567-4569
Using the method of quasielastic coherent neutron scattering by liquid lithium, the temperature dependence of self-diffusion coefficient is investigated and compared with analogous data extracted by the incoherent scattering method. 相似文献
183.
184.
《Journal of Polymer Science.Polymer Physics》2018,56(17):1193-1202
Charge transport in conjugated polymers may be governed not only by the static microstructure but also fluctuations of backbone segments. Using molecular dynamics simulations, we predict the role of side chains in the backbone dynamics for regiorandom poly(3‐alkylthiophene‐2,5‐diyl)s (P3ATs). We show that the backbone of poly(3‐dodecylthiophene‐2‐5‐diyl) (P3DDT) moves faster than that of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) as a result of the faster motion of the longer side chains. To verify our predictions, we investigated the structures and dynamics of regiorandom P3ATs with neutron scattering and solid state NMR. Measurements of spin‐lattice relaxations (T1) using NMR support our prediction of faster motion for side chain atoms that are farther away from the backbone. Using small‐angle neutron scattering (SANS), we confirmed that regiorandom P3ATs are amorphous at about 300 K, although microphase separation between the side chains and backbones is apparent. Furthermore, quasi‐elastic neutron scattering (QENS) reveals that thiophene backbone motion is enhanced as the side chain length increases from hexyl to dodecyl. The faster motion of longer side chains leads to faster backbone dynamics, which in turn may affect charge transport for conjugated polymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1193–1202 相似文献
185.
T.Kishimoto 《原子核物理评论》2009,26(Z1)
We would like to emphasize that the in-flight (K~-,N) reactions are particularly useful for the study of the K-nucleus interaction.Since the reaction mechanism is well known,there is little ambiguity to derive the K-nucleus interaction from the measured missing mass spectra.Here we discuss the missing mass spectra of the (K~-,N) reactions on the ~(12)C and ~(16)O targets.The spectra show an appreciable amount of strength below the K-nucleus threshold which indicates that the K-nuclear potential is strongly attractive.Comparison of the missing mass spectra with theoretical calculations leads to a potential depth of around-190 MeV for the ~(12)C(K~-,n) reaction.A less deep potential of around-160 MeV reproduces well that of the ~(12)C(K~-,p) reaction.The difference can be due to isospin dependence of the interaction.Our data show that the K-nucleus potential is very deep to realize kaon condensation in the core of neutron stars. 相似文献
186.
We examine the crystallization and chain conformation behavior of semicrystalline poly(ethylene oxide) (PEO) and amorphous poly(vinyl acetate) (PVAc) mixtures with wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and small‐angle neutron scattering (SANS) experiments. For blends with PEO weight fractions (wtPEO) greater than or equal to 0.3, below the melting point of PEO, the WAXD patterns reveal that crystalline PEO belongs to the monoclinic system. The unit‐cell parameters are independent of wtPEO. However, the bulk crystallinity determined from WAXD decreases as wtPEO decreases. The scattered intensities from SAXS experiments show that the systems form an ordered crystalline/amorphous lamellar structure. In a combination of WAXD and SAXS analysis, the related morphological parameters are assigned correctly. With the addition of amorphous PVAc, both the average amorphous layer thickness and long spacing increase, whereas the average crystalline layer thickness decreases. We find that a two‐phase analysis of the correlation function from SAXS, in which the scattering invariant is linearly proportional to the volume fraction of lamellar stacks, describes quantitatively the crystallization behavior of PEO in the presence of PVAc. When wtPEO is close to 1, the samples are fully spaced‐filled with lamellar stacks. As wtPEO decreases from 1.0 to 0.3, more PVAc chains are excluded from the interlamellar region into the interfibrillar region. The fraction outside the lamellar stacks, which is completely occupied with PVAc chains, increases from 0 to 58%. Because the radius of gyration of PVAc with a random‐coil configuration determined from SANS is smaller than the average amorphous layer thickness from SAXS, we believe that the amorphous PVAc chains still persist with a random‐coil configuration even when the blends form an ordered structure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2705–2715, 2001 相似文献
187.
用5台带有慢化剂(聚乙烯)的BF33正比计数管中子探测器测量中子通量和剂量当 量.4台 置于HL_1M装置的四周,分别测量了在氘等离子体条件下,因欧姆加热和波加热产生的热核聚 变中子产额、中子通量和剂量,以及氢等离子体条件下因高能x射线引起的光致核反应而产生 的光致中子. 另一台流动于其他6个观察点,主要监测中子剂量当量. 在D_D聚变条件下,实测 中子产额与计算值作比较,两者在数量级上大体一致. 中子辐射剂量当量远低于国家和部颁 标准,更低于国际防护委员会推荐的中子辐射允许剂量当量
关键词:
3正比计数管')" href="#">BF33正比计数管
光致中子
氘_氘聚变中子
剂量当量 相似文献
188.
V. K. Aswal J. V. Joshi P. S. Goyal Rajesh Patel R. V. Upadhyay R. V. Mehta 《Pramana》2004,63(2):285-290
Small-angle neutron scattering studies have been carried out to check the structural integrity of citryltrimethylammonium
bromide (CTABr) micelles in a magnetic fluid for different magnetic fluid concentrations at two different temperatures 303
and 333 K. It is found that the CTABr micelles grow with increasing magnetic fluid concentration and there is a decrease in
the micellar size with increase in temperature. 相似文献
189.
Christopher L. Soles Jack F. Douglas Wen-Li Wu 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):3218-3234
Incoherent neutron scattering is presented as a powerful tool for interpreting changes in molecular dynamics as a function of film thickness for a range of polymers. Motions on approximately nanosecond and faster timescales are quantified in terms of a mean-square atomic displacement (〈u2〉) from the Debye–Waller factor. Thin-film confinement generally leads to a reduction of 〈u2〉 in comparison with the bulk material, and this effect becomes especially pronounced when the film thickness approaches the unperturbed dimensions of the macromolecule. Generally, there is a suppression (never an enhancement) of 〈u2〉 at temperatures T above the bulk calorimetric glass-transition temperature (Tg). Below Tg, the reduction in the magnitude of 〈u2〉 depends on the polymer and the length scales being probed. Polymers with extensive segmental or local mobility in the glass are particularly susceptible to reductions of 〈u2〉 with confinement, especially at the Q vectors probing these longer length scales, whereas materials lacking these sub-Tg motions are relatively insensitive. Moreover, a reduced 〈u2〉 value correlates with reduced mobility at long time and spatial scales, as measured by diffusion in these thin polymer films. Finally, this reduced thin-film mobility is not reliably predicted by thermodynamic assessments of an apparent Tg, as measured by discontinuities or kinks in the T dependence of the thermal expansion, specific volume, index of refraction, specific heat, and so forth. These measurements illustrate that 〈u2〉 is a powerful and predictive tool for understanding dynamic changes in thin polymer films. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3218–3234, 2004 相似文献
190.
Precipitates of ceria were synthesized by homogeneous precipitation method using cerium nitrate and hexamethylenetetramine
at 80°C. The precipitates were ground to fine particles of average size ∼0.7 μm. Circular disks with 10 mm diameter, 2 and
3 mm thickness were prepared from the green compacts by sintering at 1300° C for three different sintering times. Evolution
of the pore structures in these specimens with sintering time was investigated by small-angle neutron scattering (SANS). The
results show that the peak of the pore size distribution shifts towards the larger size with increasing sintering time although
the extent of porosity decreases. This indicates that finer pores are eliminated from the system at a faster rate than the
coarser ones as sintering proceeds and some of the finer pores coalesce to form bigger ones. 相似文献