In order to study the influence of the stereoreguralities of polymer chains on the mechanical properties of films of poly(vinyl alcohol) (PVA)(VTFA) derived from vinyl trifluoroacetate, the strength of the film was measured. In the case of undrawn PVA(VTFA) films, Young's modulus and strength at break were the smallest at the annealing temperature of about 100°C. It is considered to be due to the melt of small microcrystals and the increase in mobility of chains in amorphous parts. Young's moduli of undrawn PVA(VTFA) films were in the range of 1.50–3.75 GPs and the values were higher than that (0.17–0.36 GPa) of undrawn film of commercial PVA with the low concentration of syndiotacticity and the high concentration of head-to-head bounds. In the case of drawn, annealed PVA(VTFA) films, the maximum Young's modulus was about 20 GPa. 相似文献
The poly(ethylene oxide) (PEO)-sodium thiocyanate system was found to exhibit polymorphism: there exist at least three crystal modifications. Among them, the crystal structures of two kinds of PEO-NaSCN complex with molar ratios (EO:NaSCN) of 3:1 (form I) and 1:1 (form II), respectively, were determined by X-ray diffraction. Crystal data are as follows: form I, monoclinic P21/a, a = 16.83, b = 10.64, c(chain axis)=7.19 Å°
1 Å=10−1 nm, γ=125.5° (c-unique), N=12 EO units (2 chains) and 4 NaSCN ions; form II, monoclinic P21/c, a=7.55, b=12.10, c(chain axis)=5.83 Å, β=97.5° (b-unique), N=4 EO units (2 chains) and 4 NaSCN ions. Form I has a crystal structure resembling that of the PEO-NaI complex. The polymer chains have a twofold helical structure of
conformation, the chain repeat comprising six EO units. The helical polymer chain coils around an array of Na ions and each Na ion is coordinated by four polymer O atoms and two N of the SCN ions (the coordination number is six). In form II, which exists only under high tension, the polymer chains have a glide structure of
conformation, the chain repeat comprising two EO units. Since the PEO chain in form II takes a rather stretched conformation, the Na ions are not wrapped by the polymer chain. The coordination number is again six, but each Na ion is coordinated by two polymer O atoms, two N and two S of the SCN ions. Form II is transformed into form I when the tension is released. 相似文献
Wireless mesh networks (WMNs) are cost-efficient networks that have the potential to serve as an infrastructure for advanced location-based services. Location service is a desired feature for WMNs to support location-oriented applications. WMNs are also interesting infrastructures for supporting ubiquitous multimedia Internet access for mobile or fixed mesh clients. In order to efficiently support such services and offering QoS, the optimized placement of mesh router nodes is very important. Indeed, such optimized mesh placement can support location service managed in the mesh and keep the rate of location updates low. This node location-based problem has been shown to be NP-hard and thus is unlikely to be solvable in reasonable amount of time. Therefore, heuristic methods, such as genetic algorithms (GAs), are used as resolution methods. In this paper, we deal with the effect of population size for location-aware node placement in WMNs. Our WMN-GA system uses GA to determine the positions of the mesh routers and mesh clients in the grid area. We used a location-aware node placement of mesh router in cells of considered grid area to maximize network connectivity and user coverage. We evaluate the performance of the proposed and implemented WMN-GA system for low and high density of clients considering different distributions and considering giant component and number of covered users parameters. The simulation results show that for low-density networks, with the increasing of population size, GA obtains better result. However, with the increase in the population size, the GA needs more computational time. The proposed system has better performance in dense networks like hot spots for Weibull distribution when the population size is big. 相似文献
(R)- and (S)-10,14-dimethyl-1-pentadecyl isobutyrates were synthesized from (S)- and (R)-citronellols, respectively. TheR enantiomer was as active as the natural pheromone but theS enantiomer was less active in the electrophysiological analyses, which provided conclusive proof that the absolute configuration of the natural pheromone isR. 相似文献
We developed a new series of binary vectors useful for Gateway cloning to facilitate transgenic experiments in plant biotechnology. The new system, Gateway Binary Vectors (pGWBs) realized efficient cloning, constitutive expression using the cauliflower mosaic virus (CaMV) 35S promoter and the construction of fusion genes by simple clonase reaction with an entry clone. The reporters employable in this system are beta-glucuronidase (GUS), synthetic green fluorescent protein with S65T mutation (sGFP), luciferase (LUC), enhanced yellow fluorescent protein (EYFP), and enhanced cyan fluorescent protein (ECFP). The tags available are 6xHis, FLAG, 3xHA, 4xMyc, 10xMyc, GST, T7-epitope, and tandem affinity purification (TAP). In total, 13 kinds of reporter or tag were arranged and were almost applicable to both N- and C-fusions. The pGWBs could be used for many purposes, such as promoter::reporter analysis, observation of subcellular localization by the expression of proteins fused to a reporter or tag, and analysis of protein-protein interaction by copurification and immunodetection experiments. The pGWBs were constructed with modified pBI101 containing a CaMV35S promoter-driven hygromycin phosphotransferase (HPT) gene as the second selection marker. We also constructed pGWBs with the marker HPT driven by the nopaline synthase promoter. By using the pGWB system, the expression of tagged proteins, and the localization of GFP-fused proteins were easily analyzed. Moreover, tissue-specific and inducible gene expression using a promoter was also monitored with pGWBs. It is expected that, the pGWB system will serve as a powerful tool for plasmid construction in plant research. 相似文献
We investigated the adsorption/desorption mechanism of water and the variation of water adsorption for modern and archaeological wood using near-infrared spectroscopy. A mixture model of water was used to decompose the near-infrared difference spectra into three components (free water molecules (S 0), those with one OH group engaged in hydrogen bonding (S1), and those with two OH groups engaged in hydrogen bonding (S2)) based on a principal component analysis. The variations of each water component with relative humidity could be explained by proposing a model that describes water absorption in three stages. It was concluded that the aging phenomenon in wood is due to the decrease of adsorption sites on hemicellulose and amorphous cellulose. 相似文献
The electrostatic energy in a dipolar monolayer domain with orientational deformation has been analyzed for the study of monolayer shapes. It is demonstrated that a monolayer domain is viewed as a system of interacting induced electric charges distributed at the inside and boundary of a domain. Since induced charge distribution is determined by orientational deformation and domain shape, the electrostatic energy is represented in the form of Frank splay elastic energy with spontaneous splay and curvature elastic energy with spontaneous curvature. 相似文献
Total mercury (T-Hg), methyl mercury (M-Hg), cadmium (Cd), selenium (Se), zinc (Zn) and copper (Cu) concentrations in the organs of melon-headed whales from a mass stranding on the Japanese coast were analyzed. The mean concentration of T-Hg in the liver (126+/-97 microg/wet g, n=13) was markedly higher than those in kidney (6.34+/-2.36 microg/wet g, n=12) and muscle (4.90+/-2.33 microg/wet g, n=15). In contrast, the mean concentration of M-Hg in the liver (9.08+/-2.24 microg/wet g) was similar to those in the kidney (3.47+/-0.91 microg/wet g) and muscle (3.78+/-1.53 microg/wet g). The mean percentage of M-Hg in the T-Hg found in the liver (13.1+/-10.3) was significantly lower than those in the kidney (58.3+/-15.0) and muscle (78.9+/-8.4). The molar ratio of T-Hg to Se in the liver was effectively 1.0, but those in the kidney and muscle were markedly lower. Conversely, the mean concentration of Cd was markedly higher in the kidney (24.4+/-7.4 microg/wet g) than in the liver (7.24+/-2.08 microg/wet g) and muscle (less than 0.05 microg/wet g). These results suggest that the formation of Hg-Se compounds mainly occurs in the liver after the demethylation of M-Hg, and Cd preferentially accumulates in the kidney of melon-headed whales. 相似文献