The two-tone frequency modulation spectroscopy (TTFMS) is widely used for gas trace detection with its low noise absorption signal. In this paper we propose and implement the TTFMS scheme for frequency offset locking a single diode laser to an atomic resonance line by using its dispersion signal. The TTFMS theory is first discussed under the assumption that the intermediate modulation frequency is comparable to the linewidth of the absorption feature, and the dependence of the TTFMS absorption and dispersion features on the intermediate modulation frequency and modulation index are investigated theoretically. Based on a fiber-coupled electro-optic modulator (EOM) with two-tone modulation, we experimentally demonstrated the performance of the frequency offset locking method. The result shows a short-term frequency stability of the frequency offset locked laser reached around 1.1 x 10(-11), with an averaging time of 2 s. This method can find wide applications in fields requiring widely tunable frequency offset locking a single laser to the atomic resonance line, like precision spectroscopy and Raman optics for atom interferometers.
The calculation of rate constants of addition and abstraction reactions of 2,4,4-trimethyl-l-pentene with H and O(P-3) were conducted by conventional transition state theory (TST) and canonical variational transition state theory (CVT). Potential energy surfaces of reactions were calculated at the DLPNO CCSD(T)/cc-pVTZ//M06-2X/6-311G(d,p) as well as the CCSD(T)/6-311++G(d,p)//M06-2X/6-311(d,p) level. Moreover, quantum mechanical effects were determined by multidimensional small-curvature tunneling (SCT) and zero-curvature tunneling (ZCT) methods. 2,4,4-Trimethyl-l-pentene contains primary and secondary allylic, alkylic, and vinylic H atoms. It also contains addition reactions into central and terminal carbon atom channels. The results indicated that allylic H abstraction channels dominate the overall H abstractions resulting from the lower barriers. In addition, a radical added into terminal carbon dominates the addition reactions. The branching ratio is more than 72% above 1500 K for H abstraction and more than 90% below 500 K for H addition reactions.
Mixed matrix membranes (MMMs) were fabricated by incorporating ZIF-8@GO into Pebax matrix to improve CO2 separation performance. The ZIF-8@GO played multiple roles in enhancing membrane performance. First, the high-aspect ratio GO nanosheets in polymer matrix increased the length of the tortuous path of gas diffusion, restricting the diffusion of larger molecules and favoring the diffusion of small molecules with less resistance, which enhanced the diffusivity selectivity. Second, the inherent high permeability of ZIF-8 with ultra-microporosity was anticipated to optimize fractional free volume and enhance the gas permeability and solubility selectivity of MMMs. The MMMs doped with ZIG-8@GO had better gas separation performance than those doped with only ZIF-8 or GO. The membrane containing 6 wt% of ZIF-8@GO (Peabx/ZIF-8@GO-6) exhibited the optimum performance with a CO2 permeability of 249 Barrer and a CO2/N-2 selectivity of 47.6. Compared with the pure Pebax membrane, the CO2 permeability and CO2/N-2 selectivity of the Pebax/ZIF-8@GO-6 MMMs were increased by 191% and 174%, respectively. The strategy of growing ZIFs on GO may provide an effective method to further develop MMMs performance through the modification of ZIFs on existing fillers which had larger adsorption differences to specific gases. (C) 2016 Elsevier B.V. All rights reserved.
Li, Xiaojie
Zhou, Jiajing
Dong, Xiaonan
Cheng, Wai-Yin
Duan, Hongwei
Cheung, Peter C. K.
The photothermal cancer therapeutic effect of the AuNR-Glu nanohybrids produced by coating native gold nanorods (AuNRs) with a natural mushroom biopolymer from the Pleurotus tuber-regium sclerotia (Glu) were studied in the second near-infrared window (NIR-II). The AuNR-Glu exhibited low cytotoxicity and high biocompatibility due to the surface modification of Glu when compared with the native AuNRs. AuNR-Glu nanohybrids had a high photothermal transduction efficiency (eta) of 43.12%, causing effective in vitro cell ablation in both HT-29 (94.2 +/- 0.8% cell death) and SW480 (94.8 +/- 1.1% cell death) colon cancer cells under 1064 nm NIR-II laser irradiation at 1.0 W/cm(2). Intravenous injection of AuNR-Glu nanohybrids followed by irradiation from a NIR-II laser at a safe dose (1.0 W/cm(2) for 5 min) in nude mice implanted with HT 29 tumors was effective in significantly reducing the tumor growth, with no obvious harmful side effects, as evidenced by histological analysis of major organs. The present results have shown that AuNRs modified by natural biopolymers from mushroom beta-glucans are novel nanomaterials with low cytotoxicity and effective photothermal anticancer agents with potential biomedical applications.
A previous study by our group found that electro-acupuncture (EA) at the Shenting (DU24) and Baihui (DU20) acupoints ameliorates cognitive impairment in rats with cerebral ischemia-reperfusion (I/R) injury. However, the precise mechanism of action has remained largely unknown. The present study investigated whether brain-derived neurotropic factor (BDNF) mediates hippocampal synaptic plasticity as the underlying mechanism. Rats were randomly divided into three groups: The sham operation control (Sham) group, the focal cerebral ischemia-reperfusion (I/R) group, and the I/R with EA treatment (I/R+EA) group. The I/R+EA group received EA treatment at the Shenting (DU24) and Baihui (DU20) acupoints after the operation. EA treatment was found to ameliorate neurological deficits (P<0.05) and reduce the cerebral infarct volume (P<0.01). In addition, EA improved cognitive function in cerebral I/R-injured rats (P<0.05). Furthermore, EA treatment promoted synaptic plasticity. Simultaneously, EA increased the hippocampal expression of BDNF, its high-affinity tropomyosin receptor kinase B (TrkB) and post-synaptic density protein-95 (PSD-95) in the rats with cerebral I/R injury. Collectively, the findings suggested that BDNF-mediated hippocampal synaptic plasticity may be one mechanism via which EA treatment at the Shenting (DU24) and Baihui (DU20) acupoints improves cognitive function in cerebral I/R injured rats.
Interactions between endophytic bacterial communities and hyperaccumulators in heavy metal-polluted sites are not fully understood. In this study, the diversity of stem-associated endophytic bacterial communities of two hyperaccumulators (Solanum nigrum L. and Phytolacca acinosa Roxb.) growing in mine soils was investigated using molecular-based methods. The denaturing gradient gel electrophoresis (DGGE) analysis showed that the endophytic bacterial community structures were affected by both the level of heavy metal pollution and the plant species. Heavy metal in contaminated soil determined, to a large extent, the composition of the different endophytic bacterial communities in S. nigrum growing across soil series (five sampling spots, and the concentration of Cd is from 0.2 to 35.5 mg/kg). Detailed analysis of endophytic bacterial populations by cloning of 16S rRNA genes amplified from the stems of the two plants at the same site revealed a different composition. A total of 51 taxa at the genus level that included alpha-, beta-, and gamma-Proteobacteria (68.8% of the two libraries clones), Bacteroidetes (9.0% of the two libraries clones), Firmicutes (2.0% of the two libraries clones), Actinobacteria (16.4% of the two libraries clones), and unclassified bacteria (3.8% of the two libraries clones) were found in the two clone libraries. The most abundant genus in S. nigrum was Sphingomonas (23.35%), while Pseudomonas prevailed in P. acinosa (21.40%). These results suggest that both heavy metal pollution and plant species contribute to the shaping of the dynamic endophytic bacterial communities associated with stems of hyperaccumulators. =20
Molecular dynamic model of nanofluid between flat plates under shear flow conditions was built. The nanofluid model consisted of 12 spherical copper nanoparticles with each particle diameter of 4 nm and argon atoms as base liquid. The Lennard-Jones (LJ) potential function was adopted to deal with the interactions between atoms. Thus, the motion states of nanoparticles during the process of flowing were obtained and the flow behaviors of nanofluid between flat plates at different moments could be analyzed. The simulation results showed that an absorption layer of argon atoms existed surrounding each nanoparticle and would accompany with the particle to move. The absorption layer contributed little to the flow of nanoparticles but much to the heat transferring in nanofluids. Another phenomenon observed during shear flowing process was that the nanoparticles would vibrate and rotate besides main flowing with liquid argon and these micro-motions could strengthen partial flowing in nanofluids.
Hpa1 is a harpin protein produced by Xanthomonas oryzae, an important bacterial pathogen of rice, and has the growth-promoting activity in plants. To understand the molecular basis for the function of Hpa1, we generated an inactive variant protein, Hpa1 delta NT, by deleting the nitroxyl-terminal region of the Hpa1 sequence and compared Hpa1 delta NT with the full-length protein in terms of the effects on vegetative growth and related physiological responses in Arabidopsis. When Hpa1 was applied to plants, it acted to enhance the vegetative growth but did not affect the floral development. Enhanced plant growth was accompanied by induced expression of growth-promoting genes in plant leaves. The growth-promoting activity of Hpa1 was further correlated with a physiological consequence shown as promoted leaf photosynthesis as a result of facilitated CO2 conduction through leaf stomata and mesophyll cells. On the contrary, plant growth, growth-promoting gene expression, and the physiological consequence changed little in response to the Hpa1 delta NT treatment. These analyses suggest that Hpa1 requires the nitroxyl-terminus to facilitate CO2 transport inside leaf cells and promote leaf photosynthesis and vegetative growth of the plant. =20