Syntheses, structures and Raman spectra of Cd(BF4)(AF6) (A = Ta, Bi) compounds

The compounds, Cd(BF₄)(TaF₆) and Cd(BF₄)(BiF₆), have been synthesized and characterized by single-crystal X-ray diffraction and Raman spectroscopy. Both isostructural compounds crystallize in the monoclinic P2₁/c space group with a = 8.2700(6) Å, b = 9.3691(6) Å, c = 8.8896(7) Å, β = 94.196(3)°, V = 686.94(9) Å³ for Cd(BF₄)(TaF₆) and a = 8.3412(8) Å, b = 9.4062(8) Å, c = 8.9570(7) Å, β = 93.320(5)°, V = 701.58(11) Å³ for Cd(BF₄)(BiF₆). Eight fluorine atoms (4 BF₄⁻ + 4 AF₆⁻) form a surrounding around the cadmium atom in the shape of distorted square antiprism. These compounds are not isostructural with mixed-anion analogues of Ca, Sr, Ba and Pb studied earlier.     

Assessing the MALDI-TOF MS sample preparation procedure to analyze the influence of thermo-oxidative ageing and thermo-mechanical degradation on poly (Lactide)

Multiple processing by means of successive injection cycles was used to simulate the thermo-mechanical degradation effects on the oligomeric distribution of PLA under mechanical recycling. Likewise, an accelerated thermal ageing over PLA glass transition was performed in order to simulate its service life. MALDI-TOF MS was used for the analysis and the sample preparation procedure was assessed by means of a statistical Design of Experiments (DoE). The quality effects in use for the analysis were signal-to-noise ratio and Resolution. Different matrixes, analyte/matrix proportions and the use of NaTFA as cationization agent were considered. A deep inspection of the statistical results provided a better understanding of the influence of the different factors, individually or in combination, to the signal. The application of DoE for the improvement of the MALDI measurement of PLA stated that the best combination of factors (levels) was the following: matrix (s-DHB), proportion analyte/matrix (1/5 V/V), and no use of cationization agent. Degradation primarily affected the initially predominant cyclic [LA_C]_n and linear H[LA_L]_nOH species, where LA stands for a PLA repeating unit. Intramolecular and intermolecular transesterifications as well as hydrolytic and homolytic reactions took place during the formation and disappearance of oligomeric species. In both degradation mechanisms induced by thermal ageing and thermo-mechanical degradation, the formation of H[LA_L]_nOCH₃ by intermolecular transesterifications was highlighted.     

Titania immobilized polypropylene hollow fiber as a disposable coating for stir bar sorptive extraction-high performance liquid chromatography-inductively coupled plasma mass spectrometry speciation of arsenic in chicken tissues

The bottleneck of applying stir bar sorptive extraction (SBSE) to elemental speciation analysis is lack of suitable extraction phases with good affinities to different elemental species. In this paper, a newly high polar extraction phase of titania immobilized polypropylene hollow fiber (TiO₂-PPHF) was prepared by sol–gel immersion and low temperature hydrothermal process and the obtained TiO₂-PPHF inherits the adsorption properties of TiO₂ and the toughness of PPHF. With a suitable size of stainless steel magnetic bar inserted into the prepared TiO₂-PPHF, a disposable TiO₂-PPHF coating stir bar was obtained. The prepared TiO₂-PPHF was characterized by X-ray diffraction spectrometry and scanning electron microscopy and the significant parameters affecting the extraction efficiency of different arsenic species were studied. Based on the above facts, a new method of SBSE combined with high performance liquid chromatography (HPLC)–inductively coupled plasma mass spectrometry (ICP-MS) was developed for the speciation of phenyl arsenic compounds and their possible transformation products in chicken tissues. Under the optimal conditions, limits of detection (LODs) of the developed method for eight target arsenic species were in the range of 11.4–64.6 ng L⁻¹ with enrichment factors of 8.5–22.3 (theory enrichment factor was 50), and the relative standard deviations (RSDs) were varying from 6.3 to 12.6% (c_AsIII/V = 5 μg L⁻¹, c_{MMA,DMA,p-ASA,4-OH,3-NHPAA,PA,4-NPAA} = 10 μg L⁻¹, n = 7). The proposed method was successfully applied to the speciation of arsenic in chicken meat/liver samples and the recoveries for the spiked samples were in the range of 78.5–120.4%. In order to validate the accuracy of the proposed method, a certified reference material of BCR-627 tuna fish tissue was analyzed and the determined values were in good agreement with the certified values. The TiO₂-PPHF was demonstrated to be a highly selective coating for the target arsenic species, and could be easily prepared in batches with low cost. In addition, with the disposable coating, the carry-over effect commonly encountered in conventional SBSE was avoided.     

Synthesis, crystal structures and photoluminescence properties of new oxyborates, Mg5NbO3(BO3)3 and Mg5TaO3(BO3)3, with novel warwickite-type superstructures

Single crystals of new oxyborates, Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃, were prepared at 1370 °C in air using B₂O₃ as a flux. They were colorless and transparent with block shapes. X-ray diffraction analysis of the single crystals revealed Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃ to be isostructural. The X-ray diffraction reflections were indexed to the orthorhombic Pnma (No. 62) system with a=9.3682(3) Å, b=9.4344(2) Å, c=9.3379(3) Å and Z=4 for Mg₅NbO₃(BO₃)₃ and a=9.3702(3) Å, b=9.4415(3) Å, c=9.3301(2) Å and Z=4 for Mg₅TaO₃(BO₃)₃. The crystal structures of Mg₅NbO₃(BO₃)₃ and Mg₅TaO₃(BO₃)₃ are novel warwickite-type superstructures having ordered arrangements of Mg and Nb/Ta atoms. Polycrystals of Mg₅NbO₃(BO₃)₃ prepared by solid state reaction at 1200 °C in air showed broad blue-to-green emission with a peak wavelength of 470 nm under 270 nm ultraviolet excitation at room temperature.     

Yangian symmetry in molecule {V6} and four-spin Heisenberg model

The symmetry operator Q = Y² is introduced to re-describe the Heisenberg spin triangles in the {V6} molecule, where Y stands for the Yangian operator which can be viewed as special form of Dzyaloshinsky–Moriya (DM) interaction for spin 1/2 systems. Suppose a parallelogram Heisenberg model that is comprised of four -spins commutes with Q, which mean that it possesses Yangian symmetry, we show that the ground state of the Hamiltonian H₄ for the model allows to take the total spin S = 1 by choosing some suitable exchange constants in H₄. In analogy to the molecule {V6} where the two triangles interact through Yangian operator we then give the magnetization for the theoretical molecule “{V8}” model which is comprised of two parallelograms. Following the example of molecule {V15}, we give another theoretical molecule model regarding the four -spins system with total spin S = 1 and predict the local moments to be , respectively.     

Effects of different binders on microstructure and phase composition of hydroxyapatite Nd-YAG laser clad coatings

The laser clad coating technique can help to produce metallurgical bonding with high bonding strength between the coating layer and the substrate, which has been gradually applied for hydroxyapatite (HA) coating on metallic substrates. In this study, HA powder is mixed with two different binders, namely water glass (WG) and polyvinyl alcohol (PVA), respectively, and is then clad on Ti-6Al-4V substrates using an Nd:YAG laser system under various processing conditions. The microstructure, chemical composition and hardness of the coating layer and transition layer of the various samples are then systematically explored. The experimental results show that the coating layers of the various samples all contain both cellular dendrites and rod-like piled structures, while the transition layers contain only cellular dendrites. For all samples, the coating layer consists mostly of CaTiO₃, Ca₂P₂O₇, CaO and HA phases, whereas the transition layer contains primarily CaTiO₃, Ca₂P₂O₇, Ti₃P, Ti and HA phases. In addition, the transition layer of the WG samples also contains SiO₂ and Si₂Ti phases. In all of the specimens, the transition layer has a higher average hardness than the substrate or coating layer. Moreover, the transition layer in the WG sample is harder than that in the PVA sample.     

esfMRI of the upper STS: further evidence for the lack of electrically induced polysynaptic propagation of activity in the neocortex

Combining electrical stimulation with fMRI (esfMRI) has proven to be an important tool to study the global effects of electrical stimulation on neural networks in the brain. Here we extend our previous studies to stimulating the upper superior temporal sulcus (STS) in the anesthetized monkey. Our results show that stimulating area V5/MT and surrounding areas leads to positive BOLD responses in the majority of cortical areas known to receive direct/monosynaptic connections from the stimulation site. We confirm our previous results from stimulating primary visual cortex that the propagation of electrically induced activity is limited in its transsynaptic propagation to the first synapse also for extrastriate areas.     

Mg-TM-H (TM=Sc,Ti, V,Y, Zr,Nb)晶体形成能力和电子性能

基于密度泛函理论的第一性原理的Vienna Ab initio Simulation Package (VASP)软件系统研究了Mg₇TMH₁₆ (TM=Sc, Ti, V, Y, Zr, Nb)的晶体结构和电子性能. 分析了结合能和形成焓,计算得到的结合能显示Mg₇TiH₁₆和Mg₇NbH₁₆的稳定性最强,形成焓的变化表明Mg₇TMH₁₆具有比MgH₂更低的分解温度,电子态密度显示Mg₇TMH₁₆表现出明显的金属特性. 关键词： 第一原理 7TMH₁₆ (TM=Sc,Ti,V,Y,Zr,Nb)')" href="#">Mg₇TMH₁₆ (TM=Sc,Ti,V,Y,Zr,Nb) 结合能 形成焓     

混合溶剂对溶胶-凝胶法制备的Li3V2(PO4)3/C高倍率性能的影响

以有机-水为混合溶剂, 采用溶胶-凝胶法制备锂离子电池正极材料Li₃V₂(PO₄)₃/C, 选取乙醇、乙二醇和1,2-丙二醇为有机溶剂, 聚丙烯酸(PAA)为碳源和螯合剂. 通过X射线衍射(XRD)、扫描电镜(SEM)、恒流充放电以及循环伏安测试等方法, 研究了产物的结构形貌及电化学性能. XRD测试结果表明所有溶剂制备的样品结晶良好, 有机溶剂的加入不影响Li₃V₂(PO₄)₃材料的晶型结构. 恒流充放电结果表明有机溶剂的加入改善了材料的电化学性能. 以1,2-丙二醇-水为溶剂的样品电化学性能最好, 在3.0-4.5 V电压范围内, 0.1C (1C=150 mA·g^-1)倍率首次放电比容量为132.89 mAh·g^-1, 10C倍率首次放电比容量达125.42 mAh·g^-1, 循环700周后容量保持率为95.79%, 具有良好的倍率性能与循环性能; 在3.0-4.8 V电压范围内倍率性能较差. 扫描电镜结果表明混合溶剂制备的样品呈片状和针状, 这种形状有利于锂离子的扩散, 因此提高了材料的电化学性能.     

Chemical Speciation of Antimony(III and V) in Water by Adsorptive Cathodic Stripping Voltammetry Using the 4‐(2‐Thiazolylazo) – Resorcinol

A simple adsorptive cathodic stripping voltammetry method has been developed for antimony (III and V) speciation using 4‐(2‐thiazolylazo) – resorcinol (TAR). The methodology involves controlled preconcentration at pH 5, during which antimony(III) – TAR complex is adsorbed onto a hanging mercury drop electrode followed by measuring the cathodic peak current (I_p,c) at ?0.39 V versus Ag/AgCl electrode. The plot of I_p,c versus antimony(III) concentration was linear in the range 1.35×10^?9–9.53×10^?8 mol L^?1.The LOD and LOQ for Sb(III) were found 4.06×10^?10 and 1.35×10^?9 mol L^?1, respectively. Antimony(V) species after reduction to antimony(III) with Na₂SO₃ were also determined. Analysis of antimony in environment water samples was applied satisfactorily.