Coumarin (C9H6O2) and coumarin derivative, coumarin 6H (C15H15NO2) samples were observed with a polarizing microscope at and around the melting points. The states of the two samples are crystalline at room temperature. When the temperature of the Coumarin sample was raised and a part was melted, the crystalline phases coexisted with the liquid phase. The crystal surface coexisting with the liquid phase went through a repetition of melting and crystallization on slightly modulating the sample temperature. The two-phase coexisting state was observed with a digital camera attached to a microscope. The changes in the number of pixels in the crystal part of the photographed image showed Debye relaxation with temperature change. It was found that the relaxation time was 4.9 s when the number of pixels decreased due to surface melting or increased due to surface crystallization. This relaxation time was in good agreement with that of the dynamic-specific heat measured by AC calorimetry. The coumarin 6H microcrystal also coexisted with the melt in a temperature range at and around the melting point. The change in the number of pixels of the coumarin 6H crystal part showed Debye relaxation with respect to the temperature, and the relaxation time was 15 s, which was the same as the relaxation time of the dynamic-specific heat measured in the melting temperature range of coumarin 6H.
Polyethylene was prepared by γ-ray-induced polymerization in the temperature range 0–180°C. The morphology and the physical properties of the polymer as polymerized were studied by electron microscopy, differential scanning calorimetry, and gel permeation chromatography. Aggregates of small lamellar crystals with irregularly growing faces were produced below 55°C. Aggregates of large spherical particles were formed above 60°C together with hemispherical particles which adhered to the substrate. A few lamellar crystals of triangular or amoeba-like shapes were also found above 55°C. The polymers formed below 55°C showed a sharp single endothermic DSC peak and a bimodal molecular-weight distribution, while the sample above 60°C had a double endotherm and a unimodal molecular-weight distribution. These facts suggest that the mechanism of crystallization during polymerization below 55°C is different from that above 60°C. The melting point, however, decreased continuously with increasing polymerization temperature and was much lower than that of extended-chain crystals. The results show that the polyethylene, as polymerized, is composed of folded-chain crystals irrespective of the reaction temperature. 相似文献
We study central hyperplane arrangements with integral coefficients modulo positive integers q. We prove that the cardinality of the complement of the hyperplanes is a quasi-polynomial in two ways, first via the theory
of elementary divisors and then via the theory of the Ehrhart quasi-polynomials. This result is useful for determining the
characteristic polynomial of the corresponding real arrangement. With the former approach, we also prove that intersection
lattices modulo q are periodic except for a finite number of q’s.
This work was supported by the MEXT and the JSPS. 相似文献
A series of Ni(4) cubane complexes with the composition [Ni(hmp)(ROH)Cl](4) complexes 1-4 where R= -CH(3) (complex 1), -CH(2)CH(3) (complex 2), -CH(2)CH(2)(C(4)H(9)) (complex 3), -CH(2)CH(2)CH(2)(C(6)H(11)) (complex 4), hmp(-) is the anion of 2-hydroxymethylpyridine, t-Buhmp(-) is the anion of 4-tert-butyl-2-hydroxymethylpyridine, and dmb is 3,3-dimethyl-1-butanol] and [Ni(hmp)(dmb)Br](4) (complex 5) and [Ni(t-Buhmp)(dmb)Cl](4) (complex 6) were prepared. All six complexes were characterized by dc magnetic susceptibility data to be ferromagnetically coupled to give an S = 4 ground state with significant magnetoanisotropy (D approximately equal to -0.6 cm(-1)). Magnetization hysteresis measurements carried out on single crystals of complexes 1-6 establish the single-molecule magnet (SMM) behavior of these complexes. The exchange bias observed in the magnetization hysteresis loops of complexes 1 and 2 is dramatically decreased to zero in complex 3, where the bulky dmb ligand is employed. Fast tunneling of magnetization is observed for the high-symmetry (S(4) site symmetry) Ni(4) complexes in the crystal of complex 3, and the tunneling rate can even be enhanced by destroying the S(4) site symmetry, as is the case for complex 4, where there are two crystallographically different Ni(4) molecules, one with C(2) and the other with C(1) site symmetry. Magnetic ordering temperatures due to intermolecular dipolar and magnetic exchange interactions were determined by means of very low-temperature ac susceptibility measurements; complex 1 orders at 1100 mK, complex 3 at 290 mK, complex 4 at approximately 80 mK, and complex 6 at <50 mK. This confirms that bulkier ligands correspond to more isolated molecules, and therefore, magnetic ordering occurs at lower temperatures for those complexes with the bulkiest ligands. 相似文献
Lewis base catalyzed Mannich-type reaction between trimethylsilyl enol ethers and N-tosylaldimines is described. Nitrogen anions generated from amides or imides such as lithium benzamide or potassium phthalimide are found to be effective Lewis base catalysts in DMF at room temperature to afford the corresponding beta-amino carbonyl compounds in good to high yields; the oxygen anion generated from carboxylic acids such as lithium acetate was also found to be effective in dry DMF. The above-mentioned lithium acetate-catalyzed Mannich-type reaction between aldimines and various trimethylsilyl (TMS) enol ethers such as silyl ketene acetal proceeded smoothly even in water-containing DMF. Then, Lewis base catalyzed three-component Mannich-type reactions of TMS enol ether, tosylamide, and aromatic aldehyde having electron-withdrawing group such as p-nitrobenzaldehyde were investigated. The reaction proceeded smoothly to afford the corresponding beta-amino ester in good yield. Further, ammonium carboxylates such as tetrabutyl ammonium acetate or tetrabutyl ammonium benzoate were found to be more effective Lewis base catalysts in the above-mentioned Mannich-type reaction. The synthesis proceeded in various solvents at lower temperatures. The reaction between aldimines and TMS enol ethers generated from thioester and various ketones such as propiophenone or cyclohexanone also proceeded smoothly to afford the corresponding beta-amino carbonyl compounds in high yields with good to high anti-selectivities. 相似文献
The dependence of electron spin g-factor on magnetic field has been investigated in GaAs/AlGaAs quantum wells. We have estimated the electron g-factor from spin precession frequency in time-resolved photoluminescence measurements under a magnetic field in different configurations; the magnetic field perpendicular (g⊥) and parallel (g∥) to the quantum confinement direction. When the angle between the magnetic field and the confinement direction is 45°, we have found that g-factor varies depending on the direction of magnetic field and the circular polarization type of excitation light (σ+ or σ?). These dependences of g-factor exhibit main features of Overhauser effect that nuclear spins react back on electron spin precession. The value of g⊥ and g∥ corrected for the nuclear effects agree well with the results of four-band k·p perturbation calculations. 相似文献
We investigated three amino derivatives of ortho-aminobenzoic or anthranilic acid (o-Abz): a) 2-Amino-benzamide (AbzNH2); b) 2-Amino-N-methyl-benzamide (AbzNHCH3) and c) 2-Amino-N-N′-dimethyl-bezamide (AbzNH(CH3)2), see Scheme 1. We describe the results of ab-initio calculations on the structural characteristics of the compounds and experimental studies
about solvent effects in their absorption and steady-state and time-resolved emission properties. Ab-initio calculations showed
higher stability for the rotameric conformation in which the oxygen of carbonyl is near to the nitrogen of ortho-amino group. The derivatives present decrease in the delocalization of π electron, and absorption bands are blue shifted
compared to the parent compound absorption, the extent of the effect increasing from to Abz-NH2 to Abz-NHCH3 Abz-NH(CH3)2. Measurements performed in several solvents have shown that the the dependence of Stokes shift of the derivatives with the
orientational polarizability follows the Onsager-Lippert model for general effects of solvent. However deviation occurred
in solvents with properties of Bronsted acids, or electron acceptor characteristics, so that hydrogen bonds formed with protic
solvents predominates over intramolecular hydrogen bond. In most solvents the fluorescence decay of AbzNH2 and AbzNHCH3 was fitted to a single exponential with lifetimes around 7.0 ns and no correlation with polarity of the solvent was observed.
The fluorescence decay of AbzN(CH3)2 showed lifetimes around 2.0 ns, consistent with low quantum yield of the compound. The spectroscopic properties of the monoamino
derivative AbzNHCH3 are representative of the properties presented by Abz labelled peptides and fatty acids previously studied. 相似文献