Selection of crude Solidago virgaurea L. ssp. extracts based on two fast and efficient chromatographic methods (high-performance thin-layer chromatography or high-performance liquid chromatography) for the quantification of total saponins

JPC – Journal of Planar Chromatography – Modern TLC - A previous study on Solidago virgaurea extracts showed an inhibiting activity of Candida albicans yeast—hyphal transition due...     

Compact Difference Schemes for the Multidimensional Klein–Gordon Equation

Differential Equations - Stable compact difference schemes of $$4+2$$ and $$4+4 $$ approximation orders are considered and studied on standard stencils for the multidimensional Klein–Gordon...     

Analysis of expanded mixed finite element methods for the generalized forchheimer flows of slightly compressible fluids

The nonlinear Forchheimer equations are used to describe the dynamics of fluid flows in porous media when Darcy's law is not applicable. In this article, we consider the generalized Forchheimer flows for slightly compressible fluids, and then study the expanded mixed finite element method applied to the initial boundary value problem for the resulting degenerate parabolic equation for pressure. The bounds for the solutions, time derivative, and gradient of solutions are established. Utilizing the monotonicity properties of Forchheimer equation and boundedness of solutions, a priori error estimates for solution are obtained in ‐norm, ‐norm as well as for its gradient in ‐norm for all . Optimal ‐error estimates are shown for solutions under some additional regularity assumptions. Numerical results using the lowest order Raviart–Thomas mixed element confirm the theoretical analysis regarding convergence rates. Published 2015. Numer Methods Partial Differential Eq 32: 60–85, 2016     

Femtosecond laser pulse generation with a fiber taper embedded in carbon nanotube/polymer composite

We propose and demonstrate a new saturable absorber based on a fiber taper embedded in a carbon nanotube/polymer composite. Greater than a 10% reduction in absorption (due to saturation) is directly measured for our saturable absorber. Using an embedded fiber-taper saturable absorber, we built an all-fiber mode-locked ring laser, which produces 594 fs/1.7 nJ pulses with a repetition rate of 13.3 MHz.     

Combined Optimal Stopping and Singular Stochastic Control

In this article, a simple of combined singular stochastic control and optimal stopping in the jump-diffusion model is formulated and solved. We give sufficient conditions for the existence of an optimal strategy which has the same form as in continuous case given by Davis and Zervos [3 Davis , M.H.A. , and Zervos , M. 1994. A problem of singular stochastic control with discretionary stopping. Annals of Applied Probility 4(1):226–240. [Google Scholar]] and also Karatzas et al. [5 Karatzas , I. , Ocone , D. , Wang , H. , and Zervos , M. 2000 . Finite-fuel singular control with discretionary stopping . Stochastics and Stochastics Reports 71 : 1 – 50 .[Taylor & Francis Online] , [Google Scholar]]. This result is applied to solve explicitly an example of such problem.     

Active Q switching of a fiber laser with a microsphere resonator

We propose and demonstrate an active Q-switched fiber laser using a high-Q microsphere resonator as the Q-switching element. The laser cavity consists of an Er-doped fiber as the gain medium, a glass microsphere reflector (coupled through a fiber taper) at one end of the cavity, and a fiber Bragg grating reflector at the other end. The reflectivity of the microsphere is modulated by changing the gap between the microsphere and the fiber taper. Active Q switching is realized by oscillating the microsphere in and out of contact with the taper. Using this novel technique, we have obtained giant pulses (maximum peak power approximately 102 W, duration approximately 160 ns) at a low pump-power threshold (approximately 3 mW).     

Stir Bar Sorptive Extraction and LC–MS/MS for Trace Analysis of UV Filters in Different Water Matrices

A simple, selective and highly sensitive method was developed and optimized to determine the most commonly used UV filters with endocrine-disrupting potential in water, namely benzophenone-3 (BP-3), octocrylene (OC), ethylhexyl dimethyl p-aminobenzoate (OD-PABA), ethylhexyl methoxycinnamate, ethylhexyl salicylate (EHS) and homosalate (HMS). Samples were extracted by stir bar sorptive extraction followed by liquid desorption (SBSE-LD). The important factors influencing SBSE-LD were optimized. Under optimal conditions, assays were performed on 50 mL of water sample using stir bars (0.5 mm in film thickness, 10 mm in length) at room temperature. The analytes were determined by liquid chromatography–tandem mass spectrometry with triple quadrupole analyzer using atmospheric pressure chemical ionization. The main parameters in HPLC–APCI–MS/MS were also optimized to provide the best performances for all analytes. Moreover, matrix effect was investigated using two methods the post-column infusion system and the method of spiked matrices after extraction. As a result, no significant matrix effect on the analysis was observed. The method showed good linearity (R ² coefficients greater than 0.996 in different water samples after SBSE-LD). Recoveries of the analytes were close to 90%, except for BP-3 (64%) and OC (76%) with relative standard deviation lower than 11%. Detection limits were between 0.6 and 3.3 ng L⁻¹ for all the analytes except for HMS (94 ng L⁻¹) and EHS (114 ng L⁻¹). This methodology was applied to measure UV filters in seawater, river water and wastewater in different sites of Liguria; BP-3 and OC were found in most of the considered samples at rather low concentration level.