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41.
The free radical solution polymerization of n-octyl methacrylate has been studied in benzene-d 6 in the presence of 2,2′-azobisisobutyronitrile as thermal initiator. An on-line nuclear magnetic resonance spectroscopy was applied to record the reaction data and to determine the monomer conversion at different times during the polymerization reaction. Effect of monomer and initiator concentration as well as reaction temperature on polymerization rate was studied. The order of the reaction with respect to initiator (0.45) was consistent with the classical kinetic rate equation, while the order of reaction with respect to monomer (1.87) was much greater than unity. An overall activation energy (E a = 53.8 kJ/mol) was obtained over the temperature range 328?338 K. Also, the efficiency of the synthesized poly(n-octyl methacrylate) for improving the viscosity index of the lube oil was investigated.  相似文献   
42.
Long chain aliphatic alcohols have been used as model compounds to develop a preparative method for a water-soluble material, which could be a carrier for triacontanol, a highly hydrophobic plant growth regulator. New polyesters from long chain aliphatic (C = 12, 18 and 22) mono-1-alkyl citrates and poly(ethylene glycol) were synthesized and characterized by NMR spectroscopy. The polyester containing the triacontyl moiety was obtained from mono-1-triacontyl citrate, which was synthesized from the corresponding alcohol extracted from the Agave fourcroydes. The molecular weight of the polyesters depends on experimental conditions during synthesis such as reaction time, atmosphere, catalyst concentration and temperature. The reaction is second order in the early stage of the polyester synthesis. The reaction rate constant is independent of the length of the aliphatic chain, but it decreases with increasing of the poly(ethylene glycol) employed. Turbidity measurements have been used to study the polyester solubility. Solubility characteristics were found to depend on the of poly(ethylene glycol), the aliphatic-chain length and the value of for the polyester. These preparations could potentially be used to release triacontanol.  相似文献   
43.
The crystal structures of two single‐enantiomer amidophosphoesters with an (O)2P(O)(N) skeleton, i.e. diphenyl [(R)‐(+)‐α‐methylbenzylamido]phosphate, (I), and diphenyl [(S)‐(?)‐α‐methylbenzylamido]phosphate, (II), both C20H20NO3P, are reported. In both structures, chiral one‐dimensional hydrogen‐bonded architectures, along [010], are mediated by N—H…OP interactions. The statistically identical assemblies include the noncentrosymmetric graph‐set motif C(4) and the compounds crystallize in the chiral space group P21. As a result of synergistic co‐operation from C—H…O interactions, a two‐dimensional superstructure is built including a noncentrosymmetric R44(22) hydrogen‐bonded motif. A Cambridge Structural Database survey was performed on (O)2P(O)(N)‐based structures in order to review the frequency of space groups observed in this family of compounds; the hydrogen‐bond motifs in structures with chiral space groups and the types of groups inducing chirality are discussed. The 2,3JX–P (X = H or C) coupling constants from the NMR spectra of (I) and (II) have been studied. In each compound, the two diastereotopic C6H5O groups are different, which is reflected in the different chemical shifts and some coupling constants.  相似文献   
44.
The asymmetric unit of O,O′‐dimethyl [(2,3,4,5,6‐pentafluorophenyl)hydrazinyl]phosphonate, C8H8F5N2O3P, is composed of two symmetry‐independent molecules with significant differences in the orientations of the C6F5 and OMe groups. In the crystal structure, a one‐dimensional assembly is mediated from classical N—H…O hydrogen bonds, which includes R22(8), D(2) and some higher‐order graph‐set motifs. By also considering weak C—H…O=P and C—H…O—C intermolecular interactions, a two‐dimensional network extends along the ab plane. The strengths of the hydrogen bonds were evaluated using quantum chemical calculations with the GAUSSIAN09 software package at the B3LYP/6‐311G(d,p) level of theory. The LP(O) to σ*(NH) and σ*(CH) charge‐transfer interactions were examined according to second‐order perturbation theory in natural bond orbital (NBO) methodology. The hydrogen‐bonded clusters of molecules, including N—H…O and C—H…O interactions, were constructed as input files for the calculations and the strengths of the hydrogen bonds are as follows: N—H…O [R22(8)] > N—H…O [D(2)] > C—H…O. The decomposed fingerprint plots show that the contribution portions of the F…H/H…F contacts in both molecules are the largest.  相似文献   
45.
Recently, fractal geometry has been used as a tool for improving the detection of targets in radar systems. The fractal dimension is utilized as a feature to distinguish between target and clutter in fractal detectors. In this paper, a general model is proposed for the target and clutter signals in high resolution radar (HRR). The fractal dimensions of the clutter and the target plus clutter are evaluated. Performing statistical tests on the distribution of the fractal dimension, it is proved that a gaussian distribution can approximately model the distribution of the fractal dimension for HRR signals. The fractal detector is designed based on the gaussian distribution of the fractal dimension and its performance is compared with a semi-optimum detector. It is demonstrated that the fractal detector has great capabilities in the rejection of colored clutter. Moreover, we show that the fractal detector is CFAR, i.e., the probability of false alarm remains approximately constant in different interference powers.  相似文献   
46.
The effect of bed thickness in rectangular fluidized beds is investigated through the CFD–DEM simulations of small-scale systems. Numerical results are compared for bubbling fluidized beds of various bed thicknesses with respect to particle packing, bed expansion, bubble behavior, solids velocities, and particle kinetic energy. Good two-dimensional (2D) flow behavior is observed in the bed having a thickness of up to 20 particle diameters. However, a strong three-dimensional (3D) flow behavior is observed in beds with a thickness of 40 particle diameters, indicating the transition from 2D flow to 3D flow within the range of 20–40 particle diameters. Comparison of velocity profiles near the walls and at the center of the bed shows significant impact of the front and back walls on the flow hydrodynamics of pseudo-2D fluidized beds. Hence, for quantitative comparison with experiments in pseudo-2D columns, the effect of walls has to be accounted for in numerical simulations.  相似文献   
47.
Based on first principles calculations and the K·p effective model, we propose that alkali metal deposition on the surface of hexagonal XN2 (X= Cr, Mo, W) nanosheets induces topologically nontrivial phases in these systems. When spin orbit coupling (SOC) is disregarded, the electron-like conduction band from N-pz orbitals can be considered to cross the hole-like valence band from X-d2z orbitals, thereby giving rise to a topological nodal line state in lithium-functionalized XN2 sheets (Li2MoN2 and Li2WN2). Such band crossing is protected by the existence of mirror reflection and time reversal symmetry. More interestingly, the bands cross exactly at the Fermi level, and the linear dispersion regions of such band crossings extend to as high as 0.9 eV above the crossing. For Li2CrN2, the results reveal the emergence of a Dirac cone at the Fermi level. Our calculations show that lattice compression decreases the thickness of a Li2CrN2 nanosheet, leading to phase transition to a nodal line semimetal. The evolution of the band gap of Li2XN2 at the Γ point indicates that the nontrivial topological character of Li2XN2 nanolayers is stable over a large strain range. When SOC is included, the band crossing point is gapped out giving rise to quantum spin Hall states in Li2CrN2 nanosheets, while for Li2MoN2, the SOC-induced gap at the crossing points is negligible.  相似文献   
48.
Similarity between the gravitoelectromagnetism and the electromagnetism is discussed. We show that the gravitomagnetic field (similar to the magnetic field) can be equivalent to the non-commutative effect of the momentum sector of the phase space when one maintains only the first order of the non-commutative parameters. This is performed through two approaches. In one approach, by employing the Feynman proof, the existence of a Lorentz-like force in the gravitoelectromagnetism is indicated. The appearance of such a force is subjected to the slow motion and the weak field approximations for stationary fields. The analogy between this Lorentz-like force and the motion equation of a test particle in a non-commutative space leads to the mentioned equivalency. In fact, this equivalency is achieved by the comparison of the two motion equations. In the other and quietly independent approach, we demonstrate that a gravitomagnetic background can be treated as a Dirac constraint. That is, the gravitoelectromagnetic field can be regarded as a constrained system from the sense of the Dirac theory. Indeed, the application of the Dirac formalism for the gravitoelectromagnetic field reveals that the phase space coordinates have non-commutative structure from the view of the Dirac bracket. Particularly, the gravitomagnetic field as a weak field induces the non-trivial Dirac bracket of the momentum sector which displays the non-commutativity.  相似文献   
49.
In this study, passive cooling of a room using a solar chimney and water spraying system in the room inlet vents is simulated numerically in Yazd, Iran (a hot and arid city with very high solar radiation). The performance of this system has been investigated for the warmest day of the year (5 August) which depends on the variation of some parameters such as water flow rate, solar heat flux, and inlet air temperature. In order to get the best performance of the system for maximum air change and also absorb the highest solar heat flux by the absorber in the warmest time of the day, different directions (West, East, North and South) have been studied and the West direction has been selected as the best direction. The minimum amount of water used in spraying system to set the inside air averaged relative humidity <65 % is obtained using trial and error method. The simulation results show that this proposed system decreases the averaged air temperature in the middle of the room by 9–14 °C and increases the room relative humidity about 28–45 %.  相似文献   
50.
In this study, the application of various concentrations (0.02%, 0.04%, 0.06% and 0.08%) of Satureja khuzestanica essential oil (EO) was examined on the oxidative stability of sunflower oil and compared to butylated hydroxyanisole (BHA) during storage at 60°C. Gas chromatography (GC) and GC-mass spectrometry analyses of the oils revealed that carvacrol (87.7%) was the major component of EO. Peroxide value and anisidine value measurements in sunflower oil showed that all concentrations of EO had antioxidant effects in comparison to BHA. Oil samples supplemented with EO concentration of 0.08% were the most stable during storage (p?相似文献   
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