Using Lasers to Demonstrate the Concept of Polarizability: Variations in the Refractive Indices of the O-Halobenzenes

Using a simple 633-nm He/Ne or diode laser, the variation of the refractive indices of four ortho-substituted dihalogenated benzenes can be obtained, demonstrating the phenomenon of polarizability. In addition, this exercise is an excellent display of the correspondence between the properties of a chemical system on the macroscopic level and the characteristics of the molecule on a microscopic scale.     

Synthesis, characterization and magnetism of μ-chloranilato bi-nuclear chromium (III) complexes

Five new chloranilato-bridged binuclear chromium (III) complexes have been synthesized and identified as [Cr2(CA)L4]-(ClO4)4[L denotes 5-methyl-1,10-phenanthroline (Me-phen); 2,9-dimethyl-1, 10-phenanthroline ( Me2-phen); 5-chloro-1,10-phenanthroline(Cl-phen); diaminoethane (en) or 1,3-diaminopropane (pn)], where CA represents the dianion of chloranilic acid. Based on elemental analyses, molar conductivity and magnetic moment of room-temperature measurements, and IR and electronic spectral studies, it is proposed that these complexes have CA-bridged structures and consist of two chromium (III) ions, each in an octahedral environment. The complexes [Cr2(CA)(Me-phen)4](ClO4)4(1) and [Cr2(CA)(Me2-phen)4](ClO4)4(2) were further characterized by variable temperature (4.2-300 K) magnetic susceptibility measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, , giving the exchange parameter J = -7.8 cm-1 for (1) and J= -6.5 cm*1 for (2). This result     

Luminescence spectroscopy of high-energy 4f 11 levels of Er3+ in fluorides

The 4f¹¹ energy levels of Er³⁺ in LiYF₄ in the spectral region 39000–65000 cm^?1 have been studied. The agreement between experimental energy levels, obtained from luminescence excitation spectra, and calculated energy levels is good. Luminescence originating from high-lying energy levels has been investigated. Emission from the states ⁴D_1/2 (～47 200cm^?1), ²F(2)_7/2 (～54700cm^?1) and ²F(2)_5/2 (～63 300cm^?1) is observed. ²F(2)_5/2 emission occurs for Er³⁺ in LaF₃, where the ²F(2)_5/2 level is situated just below the lowest 4f¹⁰5d state, but also for Er³⁺ in LiYF₄, where it lies in between the two lowest 4f¹⁰5d states.     

Test of the stability of a three-phase contact line with negative line tension

The equilibrium structure of a three-phase contact line with negative line tension using a mean-field free-energy functional is calculated in the square-gradient approximation. The equilibrium density profiles are found by solving the Euler—Lagrange equations on a square grid of N ² points covering an area of L ². The fluctuations about the equilibrium structure are analysed via the spectrum of the free energy's second functional derivative. The equilibrium configuration is found to be stable with respect to fluctuations in the structure of the three-phase line and of the interfaces that meet at this line. In addition, the behaviour is investigated numerically of the lowest eigenvalue as the area of the grid is increased. The lowest eigenvalue is always positive and vanishes as 1/L ².     

Optical pumping in an organic crystal: quinoxaline in durene

Experiments have been performed to determine the path of entry into and exit from the phosphorescent triplet state T₀ of quinoxaline in a durene host. First of all the decay of phosphorescence after flash excitation was followed at 4.2 and 1.34 °K. It was found that for both perdeutero- and perhydroquinoxaline the lifetime is shortened by a factor of about three when the temperature is lowered from 4.2 to 1.34 °K. At 1.34 °K relaxation between the spin components (i.e. re-orientation of the triplet spin angular momentum) is slow relative to the decay, and the observed reduction in lifetime indicates that entry into and exit from T₀, are through the same spin component. Similar decay experiments were then carried out at 1.34 °K in a 10 kG magnetic field or in a somewhat weaker field so chosen that the effect of microwave saturation of one of the E.S.R. transitions between the components could be observed. From the results it follows that on intersystem crossing the molecules enter the manifold T₀ through the top zero-field component and thus initially have their spins aligned. Decay departs almost exclusively from the same component, even in the case of perhydroquinoxaline, where at least 45 per cent of it must be radiationless. The decay route agrees with out-of-plane polarization of phosphorescence for the free molecule. Finally, spin alignment on intersystem crossing is discussed from the theoretical point of view. It appears that the phenomenon is clear-cut only in molecules such as those of the aza-aromatics, where strong spin-orbit coupling of the atomic type occurs betwen ππ? and nπ? states.     

Phase separation in mixtures of colloidal platelets and non-adsorbing polymer: a scaled particle treatment

Scaled particle theory is used to calculate the equation of state for and the free volume accessible to a non-adsorbing polymer, represented by spheres, in a system of colloidal platelets, represented by cut spheres. At low densities the predictions agree very well with computer simulations. For infinitely thin discs, the predictions agree with existing simulation data for the isotropic phase. The analytical results are used to predict the isotropic-isotropic phase boundary as a function of platelet aspect ratio and polymer/colloid size ratio.     

罗伊氏乳杆菌NCU801对病原菌的粘附抑制性能

采用选择性平板计数法,考察罗伊氏乳杆菌NCU801活菌悬液、死菌悬液以及发酵上清液对大肠杆菌CMCC44496和金黄色葡萄球菌26003粘附Caco-2细胞的影响。结果表明:在竞争试验、排斥试验和置换试验中,罗伊氏乳杆菌NCU801活菌悬液和死菌悬液均能抑制大肠杆菌和金黄色葡萄球菌的粘附;活菌悬液比死菌悬液抑制效果更显著,其中最显著的是活菌悬液对大肠杆菌排斥抑制粘附,粘附抑制率达到(86.8±4.5)%;而发酵上清液在竞争实验中最显著,其次是置换试验,而在排斥实验中对病原菌无影响,说明发酵上清液中的细菌素能够杀死未粘附和已粘附的病原菌。更多还原     

LIGHT-INDUCED FORMATION OF O-2˙ OXYGEN RADICALS IN SYSTEMS CONTAINING CHLOROPHYLL

It has been shown recently that photosystem 1 particles, photosystem 1 lipid vesicles and chlorophyll-a lipid vesicles show identical photochemical reactions in the presence of oxygen e.g. H⁺-and O₂-uptake (Van Ginkel, 1979). Therefore, spin-trapping experiments were done to identify the oxygen radicals formed. The spintrap phenyltertiarybutylnitrone (PBN) failed to yield information about oxygen radicals. With the spintrap 5,5-dimethyl-1-pyrroline-1-oxide (DMPO), however, we obtained a mixed spectrum of O^-_2˙ and OH·-adducts generated in chloroplasts, photosystem 1 particles or chlorophyll-a lipid vesicles. These data indicate that chlorophyll-a in an artificial membrane can also catalyze O^-_2˙-formation. Chlorophyll-a lipid vesicles catalyze light-induced formation of the Tiron-semiquinone free radical, which has been proposed as a specific O^-_2˙-probe (Greenstock and Miller, 1975). However, OH· scavengers strongly reduce the formation of this radical, whereas superoxide dismutase does not. Pulse-radiolysis measurements showed that the rate constant for the reaction of Tiron with OH· is 8.2 · 10⁹M^-1 s^-1, which is considerably higher than the published Tiron/O^-_2˙ rate constants. Therefore, Tiron is a better spin probe for OH· than for O^-_2˙. We suggest that light-induced H⁺-and O^-_2˙-uptake in membranes containing chlorophyll-a in the presence of ascorbate is caused mainly by the very rapid reaction of OH· with ascorbate.     

Radiation from a Point Charge Moving through a Circular Aperture in a Screen

This paper deals with the problem of diffraction radiation froman electric point charge that moves, at a constant speed, througha circular aperture in a plane screen. The screen is assumedto be electrically perfectly conducting. The problem is reducedto the solution of an integral equation for an unknown fieldfunction in the aperture. Low-frequency solutions as well ashigh-frequency solutions are obtained. Results pertaining tothe far-field behaviour of the radiated field are given. Finally,numerical results pertaining to the radiation loss of the chargeare presented.