Impact of Electron Collision Mixing on the delay times of an electron beam excited Atomic Xenon laser

The atomic xenon (5d¿6p) infrared laser has been experimentally and theoretically investigated using a short-pulse (30-ns), high-power (1-10-MW/cm3) coaxial electron beam excitation source. In most cases, laser oscillation is not observed during the e-beam current pulse. Laser pulses of hundreds of nanoseconds duration are subsequently obtained, however, with oscillation beginning 60-800 ns after the current pulse terminates. Results from a computer model for the xenon laser reproduce the experimental values and show that oscillation begins when the fractional electron density decays below a critical value of ≈0.2-0.8×10 6. These results lend credence to the proposal that electron collision mixing of the laser levels limits the maximum value of specific power deposition that can be used to excite the atomic xenon laser efficiently on a quasi-CW basi

New Identity, New Mission: A Survey on Contemporary Migrant Workers in Beijing

Ever since the middle and late 1980s, migrant workers have started to move and work in Beijing. Compared with the old generation of migrant workers, the average age of contemporary migrant workers in Beijing is 30.71 and they are inclined to decent jobs with comparatively high education. Migrant workers with high school or above diploma account for 82.5 of the total population. More significantly, having got rid of country culture, the contemporary migrant workers have created new culture

A single chemosensor for multiple analytes: fluorogenic and ratiometric absorbance detection of Zn²⁺, Mg²⁺ and F⁻, and its cell imaging

A simple coumarin based sensor 1 has been synthesized from the condensation reaction of 7-hydroxycoumarin and ethylenediamine via the intermediate 7-hydroxy-8-aldehyde-coumarin. As a multiple analysis sensor, 1 can monitor Zn²⁺ with the fluorescence enhanced at 457 nm, and ratiometric detection at 290 nm, 350 nm and 420 nm in DMF/H₂O (1/4, v/v) medium. Sensor 1 can also monitor Mg²⁺ with the fluorescence enhanced at 430 nm, and ratiometric detection at 290 nm, 370 nm and 430 nm in DMF medium through the interaction of chelation enhance fluorescence (CHEF) with metal ions. Furthermore, 1 also can monitor F⁻ with the fluorescence enhanced at 460 nm, and ratiometric detection at 290 nm and 390 nm in DMF medium simultaneously via hydrogen bonding and deprotonation with F− anion. Spectral titration, isothermal titration calorimetry and mass spectrometry revealed that the sensor formed a 1:1 complex with Mg²⁺, Zn²⁺ or F⁻, with stability constants of 4.5 × 10⁶, 3.4 × 10⁶, 8.0 × 10⁴ M⁻1 respectively. The complexation of the ions by 1 was an exothermic reaction driven by entropy processes. Furthermore, the sensor exhibits good membrane-permeability and was capable of monitoring at the intracellular Zn²⁺ level in living cells

Structure and function of unusual Rieske-type oxygenases from human microbiota involved in carnitine metabolism

L-carnitine is an abundant nutrient in red meat, and dietary intake of L-carnitine can promote cardiovascular diseases in humans through microbial production of trimethylamine (TMA) and its subsequent oxidation to trimethylamine N-oxide by liver hepatic flavin-containing monooxygenases. Targeting gut microbial production of TMA specifically and non-lethal microbial inhibitors in general may then serve as a potential therapeutic approach for the treatment of cardiometabolic diseases. A two-component oxygenase/reductase (CntA/B) from human microbiota bacterium Acinetobacter baumannii, as well as the alternative enzyme complex YeaW/X from E. coli DH10B strain, are two groups of previously reported unusual Rieske-type proteins that cleave carnitine to produce TMA, representing an important microbial pathway of TMA production. Despite YeaW/X having 71% and 50% sequence identity to CntA and CntB, YeaW/X was found to possess broader substrate usage and could produce TMA from either choline or carnitine as substrate. We are therefore pursuing structural investigation of these enzymes to elucidate the function-structure relationships of these Rieske-type enzymes and to decipher the structural basis for broader substrate specificity of YeaW. We have cloned, expressed, and purified the CntA/B and Yea W/X enzyme complexes in order to determine crystal structures of apo and carnitine-bound forms of both of these enzyme complexes. Such studies should aid in the design of more effective inhibitors for the treatment of atherosclerosis