Weak Antilocalization and Anisotropic Magnetoresistance as a Probe of Surface States in Topological Bi2TexSe3-x Thin Films.

Topological materials, such as the quintessential topological insulators in the Bi2X3 family (X = O, S, Se, Te), are extremely promising for beyond Moore's Law computing applications where alternative state variables and energy efficiency are prized. It is essential to understand how the topological nature of these materials changes with growth conditions and, more specifically, chalcogen content. In this study, we investigate the evolution of the magnetoresistance of Bi2TexSe3-x for varying chalcogen ratios and constant growth conditions as a function of both temperature and angle of applied field. The contribution of 2D and 3D weak antilocalization are investigated by utilizing the Tkachov-Hankiewicz model and Hakami-Larkin-Nagaoka models of magnetoconductance.

Phase-Change Hyperbolic Heterostructures for Nanopolaritonics: A Case Study of hBN/VO2.

Unlike conventional plasmonic media, polaritonic van der Waals (vdW) materials hold promise for active control of light-matter interactions. The dispersion relations of elementary excitations such as phonons and plasmons can be tuned in layered vdW systems via stacking using functional substrates. In this work, infrared nanoimaging and nanospectroscopy of hyperbolic phonon polaritons are demonstrated in a novel vdW heterostructure combining hexagonal boron nitride (hBN) and vanadium dioxide (VO2 ). It is observed that the insulator-to-metal transition in VO2 has a profound impact on the polaritons in the proximal hBN layer. In effect, the real-space propagation of hyperbolic polaritons and their spectroscopic resonances can be actively controlled by temperature. This tunability originates from the effective change in local dielectric properties of the VO2 sublayer in the course of the temperature-tuned insulator-to-metal phase transition. The high susceptibility of polaritons to electronic phase transitions opens new possibilities for applications of vdW materials in combination with strongly correlated quantum materials.

Multi-mycotoxins analysis in Pheretima using ultra-high-performance liquid chromatography tandem mass spectrometry based on a modified QuEChERS method.

A sensitive and high-throughput method was established and validated for the simultaneous determination of 22 mycotoxins in Pheretima aspergillum (E.Perrier) and Pheretima guillelmi (Michaelsen). A modified Quick Easy Cheap Effective Rugged and Safe (QuEChERS) method was used for sample preparation with recoveries ranging from 73% to 105% with relative standard deviations (RSDs) <8.0% for all target analytes. Ultra-high-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UHPLC-MS/MS) was applied for separation and detection in ESI (+) and ESI (-) modes with the limits of detection (LOD) in the range of 0.05-10µgkg-1. The 22 compounds could be accurately quantified in the 0.5-1000µgkg-1 concentration range with correlation coefficients >0.99. In all cases, the intra- and inter-day precisions were lower than 6% and 10%, respectively. Matrix-matched calibration was utilized for quantification purposes to compensate for the matrix effects. Furthermore, the established method was successfully applied in 17 batches of normal real samples collected from different areas of China and 2 batches of moldy samples due to improper storage, only mold-contaminated samples were confirmed to have fumonisin B1 (FB1) and fumonisin B2 (FB2) contamination at 2.54-3.78µgkg-1. The constructed method could serve as a practical application of the UHPLC-MS/MS method for the trace analysis of multiple mycotoxins in complex matrixes, especially for those with high lipid contents.

Multi-residue analysis of pesticides in traditional Chinese medicines using gas chromatography-negative chemical ionisation tandem mass spectrometry.

In this study, a residue analysis method for the simultaneous determination of 107 pesticides in traditional Chinese medicines (TCMs), Angelica sinensis, A. dahurica, Leonurus heterophyllus Sweet, Pogostemon cablin and Lonicera japonica Thunb., was developed using gas chromatography coupled with tandem mass spectrometry in negative chemical ionisation mode (GC-NCI-MS/MS). NCI has advantages of high sensitivity and selectivity to chemicals with electron-withdrawing groups, and yields low background interference. For sample preparation, QuEChERS (quick, easy, cheap, effective, rugged and safe) was applied. Due to the unique characteristics of TCMs, the clean-up step was optimised by adjusting amounts of primary secondary amine, C18, graphitised carbon black and silica sorbents. Validation was mainly performed by determining analyte recoveries at four different spiking concentrations of 10, 50, 100 and 200 ng g(-1), with seven replicates at each concentration. Method trueness, precision, linearity of calibration curves, lowest calibrated levels (LCLs) and matrix effects were determined to demonstrate method and instrument performance. Among the 107 pesticides tested, approximately 80% gave recoveries from 80% to 110% and < 10% relative standard deviation (RSD). The LCLs for nearly all pesticides were 5 ng g(-1), and as low as 0.1 ng g(-1) for dichlofenthion, endosulfan sulphate, flumetralin, isofenphos-methyl, methyl-pentachlorophenyl sulphide and trifluralin. The results indicate that GC-NCI-MS/MS is an excellent technique for quantitative and qualitative analysis of targeted GC-amenable pesticides at ultra-trace levels, especially in complex matrices such as TCMs.

[Application of quality by design concept for the optimization of an analytical method for rhubarb anthraquinones in rat plasma].

A robust high performance liquid chromatography with fluorescence detection method (HPLC-FLD) was developed for the determination of five rhubarb anthraquinones in rat plasma using a quality by design approach. A Plackett-Burman design was utilized to screen the effects of methanol content, the pH value of mobile phase, the flow rate, column temperature, and injection volume on peak resolution, number of the theoretical plate, retention time of the last eluted peak, and tailing factor. The results showed that the methanol content in mobile phase, flow rate, and column temperature were statistically significant (p < 0.05). A Box-Behnken experimental design with response surface methodology (RSM) was then utilized to evaluate the effects of these three factors on the selected responses. Derringer' s desirability function was used for the evaluation of the chromatographic goals. The optimum conditions for separation were as follows: an isocratic mobile phase consisting of methanol/0.1% H3PO4 (81.4/18. 6, v/v), a flow rate of 1.1 mL/min, and a column temperature of 31 degrees C. The excitation and emission wavelengths were 440 nm and 540 nm, respectively. The proposed method showed good prediction ability. The results clearly showed that quality by design concept could be effectively applied to optimize the HPLC method.

Terahertz-field-induced insulator-to-metal transition in vanadium dioxide metamaterial.

Electron-electron interactions can render an otherwise conducting material insulating, with the insulator-metal phase transition in correlated-electron materials being the canonical macroscopic manifestation of the competition between charge-carrier itinerancy and localization. The transition can arise from underlying microscopic interactions among the charge, lattice, orbital and spin degrees of freedom, the complexity of which leads to multiple phase-transition pathways. For example, in many transition metal oxides, the insulator-metal transition has been achieved with external stimuli, including temperature, light, electric field, mechanical strain or magnetic field. Vanadium dioxide is particularly intriguing because both the lattice and on-site Coulomb repulsion contribute to the insulator-to-metal transition at 340 K (ref. 8). Thus, although the precise microscopic origin of the phase transition remains elusive, vanadium dioxide serves as a testbed for correlated-electron phase-transition dynamics. Here we report the observation of an insulator-metal transition in vanadium dioxide induced by a terahertz electric field. This is achieved using metamaterial-enhanced picosecond, high-field terahertz pulses to reduce the Coulomb-induced potential barrier for carrier transport. A nonlinear metamaterial response is observed through the phase transition, demonstrating that high-field terahertz pulses provide alternative pathways to induce collective electronic and structural rearrangements. The metamaterial resonators play a dual role, providing sub-wavelength field enhancement that locally drives the nonlinear response, and global sensitivity to the local changes, thereby enabling macroscopic observation of the dynamics. This methodology provides a powerful platform to investigate low-energy dynamics in condensed matter and, further, demonstrates that integration of metamaterials with complex matter is a viable pathway to realize functional nonlinear electromagnetic composites.

Directed self-assembly of epitaxial CoFe2O(4)-BiFeO3 multiferroic nanocomposites.

CoFe(2)O(4) (CFO)-BiFeO(3) (BFO) nanocomposites are an intriguing option for future memory and logic technologies due to the magnetoelectric properties of the system. However, these nanocomposites form with CFO pillars randomly located within a BFO matrix, making implementation in devices difficult. To overcome this, we present a technique to produce patterned nanocomposites through self-assembly. CFO islands are patterned on Nb-doped SrTiO(3) to direct the self-assembly of epitaxial CFO-BFO nanocomposites, producing square arrays of CFO pillars.

An easy method to monitor lactide polymerization with a boron fluorescent probe.

Fluorescence spectroscopy has been widely used to monitor different polymer processes such as polymerization kinetics, chain entanglements, and thermal transitions. The solvent-free controlled ring-opening polymerization (ROP) of lactide is significant both commercially and for research; thus, monitoring this process with a simple fluorescence method can be very useful. Here, a fluorescent dye, difluoroboron 4-methoxydibenzoylmethane (BF(2)dbmOMe) is employed to probe lactide bulk ROP by measuring the emission from solidified reaction aliquots at room temperature. It was found that, through the course of polymerization, the fluorescence of BF(2)dbmOMe in the solid-state aliquots exhibited a systematic shift from yellow to green and then to blue, accompanied by a gradual reduction in the decay lifetime. The fluorescence color change is sensitive to the monomer percent conversion, not the polymer molecular weight. On the basis of these observations and experimental data, we propose that the long-wavelength emission with perceivably longer lifetimes arises from BF(2)dbmOMe dye aggregates (ground and/or excited states), while the dissolved individual dye molecules are responsible for the blue fluorescence with a shorter lifetime. This demonstration of the utility of BF(2)dbmOMe as a fluorescent probe for lactide polymerization could have important practical implications.

Mechanochromic luminescence quenching: force-enhanced singlet-to-triplet intersystem crossing for iodide-substituted difluoroboron-dibenzoylmethane-dodecane in the solid state.

A lipid derivative of difluoroboron-iododibenzoylmethane (BF(2)dbm(I)OC(12)H(25)) was synthesized via Claisen condensation and boronation. Green photoluminescence is observed for the complex in the solid state. Unlike the previously reported difluoroboron-avobenzone (BF(2)AVB) complex, which exhibited significantly red-shifted fluorescence upon mechanical perturbation, the emission of a BF(2)dbm(I)OC(12)H(25) solid film is quenched when the sample is smeared under air but becomes orange under nitrogen. Spectroscopic and lifetime studies suggest that smearing brings the singlet excited state closer to the triplet state, thus increasing the coupling between the two states. As a result, intersystem crossing from the singlet to the triplet excited state is facilitated, and the total luminescence intensity is quenched at room temperature.

Polymorphism and reversible mechanochromic luminescence for solid-state difluoroboron avobenzone.

Difluoroboron avobenzone (BF(2)AVB), a simple boron complex of a commercial sunscreen product, exhibits morphology-dependent emission and mechanochromic luminescence in the solid state. When scratched, smeared, or even gently touched, the emission color of BF(2)AVB films is significantly red-shifted under UV excitation. In the rubbed regions, the fluorescence recovers slowly at room temperature or much faster with heating, resulting in a simple rewritable "scratch the surface" ink of potential commercial use.

[Simultaneous determination of 56 organochlorine and pyrethroid pesticides in traditional Chinese medicines by GC coupled with dual-tower and dual-column].

The paper is to report the establishment of a method for the determination of multi-residue organochlorine and pyrethroid pesticides in traditional Chinese medicines (TCMs). Fifty-six pesticides were extracted by high-speed homogenization, and then purified through gel permeation chromatography (GPC) and solid phase extraction (SPE) cartridges. The residues were simultaneously identified and quantified by GC-ECD equipped with dual tower, dual column and two micro-ECD detectors. The analytical performance was demonstrated by the analysis of 3 TCMs samples' extracts, spiked at three concentration levels for each pesticide. In general, the recoveries ranging from 70% to 110%, with relative standard deviations (RSDs) better than 15%, were obtained. The limit of detection (LOD) for most of the targeted pesticides tested was below 0.01 mg kg(-1). The method had good extraction efficiency, purification effect and good reproducibility, which could be applied to the determination of organochlorine and pyrethroid pesticide residues in the routine analysis of TCMs.

[An experimental study of immune function effect of rats irradiated with the complex field cure instrument].

The complex field cure instrument is a new medical instrument with which an experiment was carried out. Rats were continuously irradiated by the complex field for 90 days, with a day's total dose of 285.9 M.T.G. while other rats weren't irradiated for control group. The animals were respectively killed at 7d, 14d, 30d, 60d and 90d, and their blood samples were taken for cell and humoral immune analysis. The results show that values of lymphocyte transform rate, soluble receptor (SIL-2R), total hemolytic complement levels (CH50) and immunoglobulin (A.G.) after irradiation are more than those of the control group having proved that the instrument may improve immune function of rats.