Numerical analysis of the stability of optical bullets (2 + 1) in a planar waveguide with cubic–quintic nonlinearity

In this paper, we have presented a numerical analysis of the stability of optical bullets (2 + 1), or spatiotemporal solitons (2 + 1), in a planar waveguide with cubic–quintic nonlinearity. The optical spatiotemporal solitons are the result of the balance between the nonlinear parameters, of dispersion (dispersion length, L _D) and diffraction (diffraction length, L _d) with temporal and spatial auto-focusing behavior, respectively. With the objective of ensure the stability and preventing the collapse or the spreading of pulses, in this study we explore the cubic–quintic nonlinearity with the optical fields coupled by cross-phase modulation and considering several values for the non linear parameter α We have shown the existence of stable light bullets in planar waveguide with cubic–quintic nonlinearity through the study of spatiotemporal collisions of the light bullets.     

The adsorption of quaternary ammonium salts at a mercury solution interface: Part II. Non-symmetrical quaternary ammonium salts

The adsorption of triethyl alkyl (and allyl) ammonium bromides on a mercury electrode has been investigated. The isotherms and values of the free energy of adsorption yield information on the mode of adsorption of the cations. The formation of partial bimolecular films on the surface of mercury by the cations studied has been described and a simple explanation put forward concerning the mechanism of destruction of these films.     

dc resistivity of ceramic Li+Na+ beta-alumina

The dc resistivity of ceramic Li⁺Na⁺ beta-alumina is reported. The sodium electrolyte was partly exchanged with lithium and the dc resistivity measured by a four-in-line electrode arrangement using Li amalgam electrodes. The mixed alkali metal electrolyte was found to be several hundred fold more resistive than the pure sodium electrolyte, the latter being measured using sodium amalgam electrodes.     

Existence and uniqueness of solutions to a model describing miscible liquids

The existence and the uniqueness of solutions to a problem of miscible liquids are investigated in this note. The model consists of Navier–Stokes equations with Korteweg stress terms coupled with the reaction–diffusion equation for the concentration. We assume that the fluid is incompressible and the Boussinesq approximation is adopted. The global existence and uniqueness of solutions is established for some optimal conditions on the reaction source term and the external force functions.     

Surfactant‐assisted dispersive liquid–liquid microextraction of nitrazepam and lorazepam from plasma and urine samples followed by high‐performance liquid chromatography with UV analysis

Surfactant‐assisted liquid–liquid microextraction followed by high‐performance liquid chromatography with UV detection has been developed for the simultaneous preconcentration and determination of lorazepam and nitrazepam in biological fluids. In this study, an ionic surfactant (cetyltrimethyl ammonium bromide) was used as an emulsifier. The predominant parameters affecting extraction efficiency such as the type and volume of extraction solvent, the type and concentration of surfactant, sample pH, and the concentration of salt added to the sample were investigated and opted. Under the optimum conditions (extraction solvent and its volume, 1‐octanol, 70 μL; surfactant and its concentration, 1 mL of ultra‐pure water containing 2 mmol L^?1 cetyltrimethyl ammonium bromide; sample pH = 9 and salt content of 10% NaCl w/v), the preconcentration factors were obtained in the range of 202–241 and 246–265 for nitrazepam and lorazepam, respectively. The limits of quantification for both drugs were 5 μg L^?1 in water sample and 10 μg L^?1 in biological fluids with R² values higher than 0.993. The suitability of the proposed method was successfully confirmed by the extraction and determination of the target drugs in human urine and plasma samples in the range of microgram per liter.     

银纳米颗粒对铝金属在酸性介质中的耐蚀性能研究（英文）

采用材料失重、动电位极化和电化学交流阻抗技术,分别测试了温度为30 ℃,浓度为1.0 mol·L~(-1)盐酸溶液中不添加和添加银纳米颗粒时铝的腐蚀速率.结果表明,当银纳米颗粒的浓度为0.014 g·L~(-1)时,其防护效率达96.4%.随着银纳米颗粒的浓度增大,铝/溶液界面的双电层电容值减小,说明铝的表面发生了银纳米颗粒的吸附.朗缪尔吸附等温方程和动力学-热力学模型均可以较好地拟合所得到的实验数据.为了确认铝金属表面与银纳米颗粒的相互作用类型,得到了铝的零电荷电位值.研究发现,通过扫描电子显微镜和能量散射X-射线能谱分析,并结合电化学实验后铝电极表面的外观观察,可以很好地解释材料失重和电化学测试得到的数据.     

Applicability of some mass spectrometric criteria for the confirmation of pesticide residues

This study was initiated to demonstrate the impact of tolerance intervals calculated based on experimental data and standard criteria on the capability to detect and identify pesticide residues by GC-MS in plant extract. The tolerance intervals specified by the current guidelines and standards (EU, EPA, ISO, EC) result in a large number of false negative values. The tolerance intervals calculated based on the actually measured ion ratios at 2 different probability levels did not provide a better estimate. Based on experimental findings a 2-phase procedure for confirmation of pesticide residues is recommended. The first screening phase comprises identification of those pesticide residues that are likely to be present avoiding false negatives as far as possible. Relatively large tolerance intervals, +/-30% of absolute ion abundances ratios, have to be used at this point. When 2 or 3 selected ion ratios are within the established tolerance intervals the residue is confirmed. When the ions detected still indicate the possible presence of a residue the result may be reported as tentatively identified. However, when the result would lead to regulatory action, second confirmatory phase has to be undertaken. This can be achieved with the same GC-MS equipment, by injecting matrix-matched standards of the suspected analyte, in order to compensate for matrix influence on ion ratios. Alternatively, methods using different physico-chemical properties of the compound have to be used. The choice of the technique depends on their availability, time and cost.     

Characterization of Polyethylene Nascent Powders Synthesized with TpTiCl2(OR) Catalysts

Summary: Different kinds of polyethylene and ethylene-1-hexene copolymers were synthesized with TpTiCl₂(OR) (Tp = hydrotris(pyrazolyl)borate; R = Et, i-Pr, n-Bu) catalysts with and without H₂. The polymers were characterized by ¹³C NMR, capillary viscosimetry or GPC, and DSC. The homopolymers showed properties characteristic of ultra-high molecular weight polyethylenes (UHMWPE) with linear structure and high density polyethylenes (HDPE) with molecular weights in the range of commercial grades under hydrogen atmosphere. The copolymers showed a 1-hexene incorporation up to 6 mol-%. Important differences in the thermal properties were observed between the first DSC (nascent powders) and the second DSC heatings (melt-crystallized samples), which evidenced the molecular weights influence on the melt-crystallized samples.     

A convenient synthesis of pyrazolidine and 3‐amino‐6,7‐dihydro‐1H,5H‐pyrazolo[1,2‐a] pyrazol‐1‐one

A convenient four‐step synthesis of the aminobicyclopyrazolone hydrochloride 1 ·HC1 was achieved starting from di‐tert‐butyl hydrazodiformate (8) . The route entails cyclization of 8 with 1,3‐dibromopropane under phase transfer conditions followed by deprotection of 1,2‐di‐tert‐butoxycarbonylpyrazolidine (9) to give pyrazolidine hydrochloride ( 2 ·HC1). Cyanoacetylation of the latter and ring closure of the resulting cyanoacetyl pyrazolidine (7) gave 1·HC1. This novel synthesis circumvents distillation of pyrazolidine (2) and flash chromatography to provide the hydrochloride of 1 in 35–46% overall yields compared to 6% yield for the patent procedure.