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91.
The relatively low repeatability of laser-induced breakdown spectroscopy (LIBS) severely hinders its wide commercialization. In the present work, we investigate the optimization of LIBS system for repeatability improvement for both signal generation (plasma evolution) and signal collection. Timeintegrated spectra and images were obtained under different laser energies and focal lengths to investigate the optimum configuration for stable plasmas and repeatable signals. Using our experimental setup, the optimum conditions were found to be a laser energy of 250 mJ and a focus length of 100 mm. A stable and homogeneous plasma with the largest hot core area in the optimum condition yielded the most stable LIBS signal. Time-resolved images showed that the rebounding processes through the air plasma evolution caused the relative standard deviation (RSD) to increase with laser energies of > 250 mJ. In addition, the emission collection was improved by using a concave spherical mirror. The line intensities doubled as their RSDs decreased by approximately 25%. When the signal generation and collection were optimized simultaneously, the pulse-to-pulse RSDs were reduced to approximately 3% for O(I), N(I), and H(I) lines, which are better than the RSDs reported for solid samples and showed great potential for LIBS quantitative analysis by gasifying the solid or liquid samples. 相似文献
92.
Chao Y Chang P Abe K Abe K Aihara H Akai K Akatsu M Akemoto M Asano Y Aushev T Bahinipati S Bakich AM Bay A Bedny I Bitenc U Bizjak I Bondar A Bozek A Bracko M Brodzicka J Browder TE Chen A Chen KF Chen WT Cheon BG Chistov R Choi SK Choi Y Chuvikov A Dalseno J Danilov M Dash M Dragic J Drutskoy A Eidelman S Eiges V Enari Y Fang F Flanagan J Fratina S Furukawa K Gabyshev N Garmash A Gershon T Gokhroo G Golob B Haba J Hastings NC Hayasaka K Hayashii H Hazumi M Hinz L Hokuue T Hoshi Y Hou S Hou WS 《Physical review letters》2005,94(18):181803
We report the observation of the decay B0-->pi(0)pi(0), using a 253 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e(+)e(-) collider. The measured branching fraction is B(B0-->pi(0)pi(0))=(2.3(+0.4+0.2)(-0.5-0.3))x10(-6), with a significance of 5.8 standard deviations including systematic uncertainties. We also make a measurement of the direct CP violating asymmetry in this mode. 相似文献
93.
In this paper, a periodic stochastic human immunodeficiency virus (HIV) model with distributed delay and cytotoxic T lymphocytes (CTL) immune response is investigated. First, by It 's formula, we show that the solution with any positive initial value is global and positive. Then, by the stochastic comparison theorem, we obtain the sufficient conditions guaranteeing the existence and global attractivity of infection-free periodic solution. Furthermore, we discuss the existence of the infective periodic solution by Has'minskii theory. Finally, numerical examples are given to illustrate the results. 相似文献
94.
An active Q-switched diode-end-pumped Nd:YAG laser is reported with 2.9 W output power on the 4F3/2 → 4I9/2 transitions at a pump power of 24 W. With intracavity frequency doubling using a 20-mm-long LBO, a maximum blue output power of 2.25 W is achieved at a repetition rate of 23 kHz. The conversion efficiency from the corresponding Q-switched fundamental output to blue output is 96%. The peak power of the Q-switched blue pulse is up to 610 W with 160 ns pulse width. The fluctuation of the blue output power is less than 4.0% at the maximum output power. 相似文献
95.
The coexistence of TE-TM surface waves in uniaxially anisotropic left-handed materials 总被引:1,自引:0,他引:1
We investigate theoretically the characteristics of surface waves in uniaxially anisotropic left-handed materials. The constraints for the existence of TE and TM polarized surface waves in uniaxially anisotropic left-handed materials are identified. We discuss mainly whether TE and TM polarized surface modes may coexist in the same frequency domain at the interface between one isotropic regular medium and another uniaxially anisotropic left-handed medium. It is shown that the answer to the coexistence of TE and TM surface modes is really positive. The Poynting vector and the density of energy associated with surface modes are calculated. Depending on the system parameters either TE or TM surface modes has the time averaged Poynting vector directed opposite or same to the mode phase velocity. In the presence of anisotropy, negative refraction does not need to be left-handed. We show that the characteristics of surface waves in uniaxially anisotropic left-handed media are significantly different from that in isotropic left-handed media. 相似文献
96.
Carbon onions produced by DC arc discharge method were deposited on highly oriented pyrolytic graphite (HOPG) surface and their adsorption and manipulation was studied using an atomic force microscopy (AFM). Well-dispersed adsorption of carbon onions on HOPG surface was obtained and aggregations of onions were not observed. The van der Waals interaction between the onion and HOPG surface and that between two onions, were calculated and discussed using Hamaker's theory. The manipulation of adsorbed onions on HOPG surface was realized using the AFM in both the raster mode and the vector mode. The controllability and precision of two manipulation modes were compared and the vector mode manipulation was found superior, and is a useful technique for the construction of nano-scale devices based on carbon onions. 相似文献
97.
Lin Hou Yujie Yuan Junxiao Ren Yinling Zhang Yongchao Wang Xiaoning Shan Qi Liu Zhenzhong Zhang 《Journal of nanoparticle research》2017,19(8):286
In this work, carbon nanomaterials, single-walled carbon nanotubes (SWNT), graphene oxide (GO), and fullerene (C60) were modified by hyaluronic acid (HA) to obtain water-soluble and biocompatible nanomaterials with high tumor-targeting capacity and then the comparative study of these hyaluronic acid-modified carbon nanomaterials was made in vitro and in vivo. The conjugates of hyaluronic acid and carbon nanomaterials, namely, HA-SWNT, HA-GO, HA-C60, were confirmed by UV/Vis spectrum, Fourier transform infrared spectroscopy (FTIR), and a transmission electron microscope (TEM). After HA modification, the sizes of HA-SWNT, HA-GO, and HA-C60 were in a range of 70 to 300 nm, and all the three HA-modified materials were at negative potential, demonstrating that HA modification was in favor of extravasation of carbon materials into a tumor site due to enhanced permeability and retention effect of tumor. Photothermal conversion in vitro test demonstrated excellent photothermal sensitivity of HA-SWNT and HA-GO. But the reactive oxygen yield of HA-C60 was the highest compared with the others under visible light irradiation, which proved the good photodynamic therapy effect of HA-C60. In addition, cytotoxicity experiments exhibited that the inhibitory efficacy of HA-SWNT was the lowest, the second was HA-C60, and the highest was HA-GO, which was consistent with the uptake degree of them. While under the laser irradiation, the cell inhibition of the HA-SWNT was the highest, the second was HA-GO, and the last was HA-C60. In vivo evaluation of the three targeting carbon nanomaterials was consistent with the cytotoxicity assay results. Taken together, the results demonstrated that HA-SWNT and HA-GO were suited for photothermal therapy (PTT) agents for their good photothermal property, while HA-C60 was used as a kind of photodynamic therapy (PDT) agent for its photodynamic effect. 相似文献
98.
Zhihang Long Yingqing Zhan Fei Li Xinyi Wan Yi He Chunyan Hou Hai Hu 《Journal of nanoparticle research》2017,19(9):318
In this work, highly activated graphene oxide/multiwalled carbon nanotube/Fe3O4 ternary nanocomposite adsorbent was prepared from a simple hydrothermal route by using ferrous sulfate as precursor. For this purpose, the graphene oxide/multiwalled carbon nanotube architectures were formed through the π-π attractions between them, followed by attaching Fe3O4 nanoparticles onto their surface. The structure and composition of as-prepared ternary nanocomposite were characterized by XRD, FTIR, XPS, SEM, TEM, Raman, TGA, and BET. It was found that the resultant porous graphene oxide/multiwalled carbon nanotube/Fe3O4 ternary nanocomposite with large surface area could effectively prevent the π-π stacking interactions between graphene oxide nanosheets and greatly improve sorption sites on the surfaces. Thus, owing to the unique ternary nanocomposite architecture and synergistic effect among various components, as-prepared ternary nanocomposite exhibited high separation efficiency when they were used to remove the Cu (II) and methylene blue from aqueous solutions. Furthermore, the adsorption isotherms of ternary nanocomposite structures for Cu (II) and methylene blue removal fitted the Langmuir isotherm model. This work demonstrated that the graphene oxide/multiwalled carbon nanotube/Fe3O4 ternary nanocomposite was promising as an efficient adsorbent for heavy metal ions and organic dye removal from wastewater in low concentration. 相似文献
99.
100.
A simulation study of microstructure evolution during solidification process of liquid metal Ni 下载免费PDF全文
A molecular dynamics simulation study has been performed for the
microstructure evolution in a liquid metal Ni system during
crystallization process at two cooling rates by adopting the
embedded atom method (EAM) model potential. The bond-type index
method of Honeycutt--Andersen (HA) and a new cluster-type index
method (CTIM-2) have been used to detect and analyse the
microstructures in this system. It is demonstrated that the cooling
rate plays a critical role in the microstructure evolution: below the
crystallization temperature $T_{\rm c}$, the effects of cooling rate
are very remarkable and can be fully displayed. At different cooling
rates of $2.0\times10^{13}$\,K\,$\cdot$\,s$^{-1}$ and
$1.0\times10^{12}$\,K\,$\cdot$\,s$^{-1}$, two different kinds of
crystal structures are obtained in the system. The first one is the
coexistence of the hcp (expressed by (12 0 0 0 6 6) in CTIM-2) and
the fcc (12 0 0 0 12 0) basic clusters consisting of 1421 and 1422
bond-types, and the hcp basic cluster becomes the dominant one with
decreasing temperature, the second one is mainly the fcc (12 0 0 0 12
0) basic clusters consisting of 1421 bond-type, and their
crystallization temperatures $T_{\rm c}$ would be 1073 and 1173\,K,
respectively. 相似文献