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  • Hindawi Limited  (4)
  • 2015-2019  (4)
  • 1
    In: Journal of Nanomaterials, Hindawi Limited, Vol. 2019 ( 2019-02-04), p. 1-10
    Abstract: This work aimed at preparing the electrode composite LiFePO 4 @carbon by hydrothermal and the calcination process was conducted at 600, 700, and 800°C. The structure and morphology were determined by X-ray diffraction (XRD), SEM, Raman spectroscopy, X-ray photon spectroscopy (XPS), and thermal analysis. The XRD refinement’s results point out the orthorhombic structure without impurity phase and the high crystalline of synthesized olivines. The results of Raman spectroscopy and XPS confirmed the pure olivine phase as well as the successful carbon coating on the surface of olivines’ powders. Moreover, the calcinated temperature affected the morphology as well as the electrochemical performance of synthesized olivines. The electrochemical measurements were conducted by cyclic voltammetry and galvanostatic cycling test. The diffusion coefficients were calculated from cyclic voltammetry curves and reached 1.09 × 10 −12  cm 2 /s for LFP600, 2.28 × 10 −11  cm 2 /s for LFP700, and 3.27 × 10 −12  cm 2 /s LFP800. The cycling test at rate C/10 exhibited an excellent cyclability with discharge capacity of 145 mAh/g for LFP600, 170 mAh/g for LFP700, and 160 mAh/g for LFP800.
    Type of Medium: Online Resource
    ISSN: 1687-4110 , 1687-4129
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2019
    detail.hit.zdb_id: 2229480-6
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  • 2
    In: Journal of Analytical Methods in Chemistry, Hindawi Limited, Vol. 2019 ( 2019-05-08), p. 1-12
    Abstract: An ultrahigh-performance liquid chromatography in combination with high-resolution mass spectrometry Thermo Q-Extractive Focus Orbitrap MS has been introduced for analysis of multiclass pesticides in vegetable samples collected in Hanoi, Vietnam. Multiclass pesticides were separated on the Thermo Hypersil Gold PFP column utilizing a gradient of the mobile phase consisting of 5 mM ammonium formate, 0.1% formic acid in deionized water, and methanol. The target analytes were detected in the full-scan mode on Thermo Scientific Q-Exactive Focus Orbitrap MS for quantitation at the optimum operating conditions. These conditions included, but not limit to, the resolution of 70000 at the full width at half maximum in both positive and negative mode, mass range from 80 to 1000  m/z , and optimized parameters for the heated electrospray ionization source. The identification of the analytes in real samples was based on retention times, mass to charge ratios, mass accuracies, and MS/MS spectra at the confirmation mode with the inclusion list of target analytes. The mass accuracies of target analytes were from −4.14 ppm (dinotefuran) to 1.42 ppm (cinosulfuron) in the neat solvent and from −3.91 ppm (spinosad D) to 1.29 ppm (cinosulfuron) in the matrix-matched solution. Target analytes in the vegetable-based matrix were extracted by the QuEChERS method. Some critical parameters of the analytical method such as linearity, repeatability, limit of detection, and limit of quantitation have been evaluated and implemented. Excellent LOD and LOQ of the developed method were achieved at the range of 0.04–0.85 and 0.13–2.9  μ g·kg −1 , respectively. Intraday and interday repeatability of the analytical signal (peak area, n = 6 ) of the developed method were below 3% and 10%, correspondingly. The matrix effect, extraction recovery, and overall recovery were fully investigated by spiking experiments. Experimental results demonstrated that the ionization suppression or enhancement was the main contribution on the overall recoveries of target analytes. Finally, the in-house validated method was applied to pesticides screening in vegetables samples in local villages in Hanoi, Vietnam. The concentrations of all target analytes were below limit of quantitation and lower than US-FDA or EU maximum residue levels.
    Type of Medium: Online Resource
    ISSN: 2090-8865 , 2090-8873
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2019
    detail.hit.zdb_id: 2654178-6
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  • 3
    In: Journal of Analytical Methods in Chemistry, Hindawi Limited, Vol. 2019 ( 2019-04-28), p. 1-10
    Abstract: In this work, high-performance liquid chromatography in combination with inductively coupled plasma dynamic reaction cell quadrupole mass spectrometry was introduced and optimized for speciation analysis of five major arsenic species including arsenobetain (AsB), arsenite (As(III)), monomethylarsonic (MMA), dimethylarsenonic acid (DMA), and arsenate (As(V)) in rice samples. Five arsenic compounds were separated on a Hamilton PRP X100 strong anion-exchange column employed with the mobile phase that is compatible with mass spectrometry, containing ammonium carbonate, methanol, and disodium ethylenediaminetetraacetic acid. Arsenic compounds were detected online by inductively coupled plasma dynamic reaction cell quadrupole mass spectrometry utilizing oxygen as the reaction gas at a flow rate of 0.7 mL·min −1 . Five selected arsenic species were baseline separated at the optimum experimental conditions. The excellent LOD and LOQ values of the developed method were achieved in the range of 0.5 to 2.9  μ g·kg −1 and 1.7 to 9.6  μ g·kg −1 for all species of arsenic, respectively. The ionization effect in plasma during chromatographic gradient elution was systematically investigated by using postcolumn injector. Arsenic compounds in rice samples were extracted by diluted nitric acid at elevated temperature. The extraction efficiency and the interconversion of target compounds during sample preparation were also assessed. The full validation of the developed method was performed by using certified reference material, BRC 211, from European Institute of Reference and Standard for speciation analysis. The recovery of all selected arsenic species was in the range of 70 to 135.5%. The validated method was also applied to analyze rice samples collected from some contaminated rice fields. The results showed that As(III), DMA, and As(V) were found in all rice samples. Average concentration (range) of inorganic arsenic and DMA in all rice samples were 130.3 (65.5–228.1) and 32 (8.2–133.01) μ g·kg −1 , respectively. However, total concentration of inorganic arsenic in most of investigated rice samples was below the maximum residual level according to US-FDA and European Union standards.
    Type of Medium: Online Resource
    ISSN: 2090-8865 , 2090-8873
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2019
    detail.hit.zdb_id: 2654178-6
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  • 4
    Online Resource
    Online Resource
    Hindawi Limited ; 2018
    In:  International Journal of Antennas and Propagation Vol. 2018 ( 2018), p. 1-9
    In: International Journal of Antennas and Propagation, Hindawi Limited, Vol. 2018 ( 2018), p. 1-9
    Abstract: A novel wideband circularly polarized antenna array using sequential rotation feeding network is presented in this paper. The proposed antenna array has a relative bandwidth of 38.7% at frequencies from 5.05 GHz to 7.45 GHz with a highest gain of 12 dBi at 6 GHz. A corresponding left-handed metamaterial is designed in order to increase antenna gain without significantly affecting its polarization characteristics. The wideband circularly polarized antenna with 2.4 GHz of bandwidth is a promising solution for wireless communication system such as tracking or wireless energy harvesting from Wi-Fi signal based on IEEE 802.11ac standard or future 5G cellular. A potential application of this antenna as a receiving antenna for RF-DC device to obtain DC power for a wireless sensor node from Wi-Fi signal is shown.
    Type of Medium: Online Resource
    ISSN: 1687-5869 , 1687-5877
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2018
    detail.hit.zdb_id: 2397585-4
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