Optimisation of stir bar sorptive extraction and in-tube derivatisation-thermal desorption-gas chromatography-mass spectrometry for the determination of several endocrine disruptor compounds in environmental water samples

The analysis of organic pollutants in environmental water samples requires a pre-concentration step. Pre-concentration techniques such as stir bar sorptive extraction (SBSE) have gained popularity since they minimise the use of toxic organic solvents and can be considered as green analytical techniques. Similar to other pre-concentration techniques, one of the problems when SBSE is used is the matrix effect, which often occurs during the analysis of environmental water samples such as estuarine or wastewater samples. The present work studied the matrix effect during SBSE coupled to in-tube derivatisation–thermal desorption (TD)–gas chromatography–mass spectrometry for the determination of several endocrine disruptor compounds, such as alkylphenols, bisphenol A, estrogens and sterols, in environmental water samples, after optimisation of the major variables affecting the determination. Variables such as the addition of methanol or an inert salt to the donor phase, the extraction temperature, the volume of the donor phase, the stirring rate and the extraction time were studied during the SBSE optimisation. In the case of the in-tube derivatisation and TD step, the volume of the derivatisation reagent (N,O-bis(trimethylsilyl)triufloroacetamide with 1% of trimethylchlorosilane (BSTFA + 1% TMCS)) and the cryo-focusing temperature were fixed (2 μL and −50 °C, respectively) according to a consensus between maximum signal and optimal operation conditions. Good apparent recovery values (78–124%) were obtained for most of the analytes in Milli-Q water, except for 4-tert-octylphenol (4-tOP), which showed apparent recovery values exceeding 100%. Precision (n = 4) was in the 2–27%, and method detection limits were in the low nanogrammes per litre level for most of the analytes studied. The matrix effect was studied using two different approaches. On the one hand, Milli-Q water samples were spiked with humic acids, and apparent recovery values were studied with and without correction with the corresponding deuterated analogue. On the other hand, estuarine water and wastewater samples were spiked with known concentrations of target analytes, and apparent recoveries were studied as explained above. In general, the matrix effect could be corrected with the use of deuterated analogues, except for 4-tOP and nonylphenols for which [²H₄]-n-nonylphenol did not provide good corrections.     

Heteroclinic cycles arising in generic unfoldings of nilpotent singularities

In this paper we study the existence of heteroclinic cycles in generic unfoldings of nilpotent singularities. Namely we prove that any nilpotent singularity of codimension four in \mathbbR⁴{\mathbb{R}^4} unfolds generically a bifurcation hypersurface of bifocal homoclinic orbits, that is, homoclinic orbits to equilibrium points with two pairs of complex eigenvalues. We also prove that any nilpotent singularity of codimension three in \mathbbR³{\mathbb{R}^3} unfolds generically a bifurcation curve of heteroclinic cycles between two saddle-focus equilibrium points with different stability indexes. Under generic assumptions these cycles imply the existence of homoclinic bifurcations. Homoclinic orbits to equilibrium points with complex eigenvalues are the simplest configurations which can explain the existence of complex dynamics as, for instance, strange attractors. The proof of the arising of these dynamics from a singularity is a very useful tool, particularly for applications.     

In situ growth of epitaxial cerium tungstate (100) thin films

The deposition of ceria on a preoxidized W(110) crystal at 870 K has been studied in situ by photoelectron spectroscopy and low-energy electron diffraction. Formation of an epitaxial layer of crystalline cerium tungstate Ce(6)WO(12)(100), with the metals in the Ce(3+) and W(6+) chemical states, has been observed. The interface between the tungsten substrate and the tungstate film consists of WO suboxide. At thicknesses above 0.89 nm, cerium dioxide grows on the surface of Ce(6)WO(12), favoured by the limited diffusion of tungsten from the substrate.     

A water-soluble perylene dye functionalised with a 17β-estradiol: a new fluorescent tool for steroid hormones

We have successfully been able to synthesise a specific estrogen receptor-directed biolabel based on a fluorescent water-soluble perylenebisimide, thus offering great potential for determining the presence of estrogen receptors in any kind of cell. Moreover, this synthetic strategy allows the preparation of other conjugates involved in the study of any kind of receptor, simply by selecting the appropriate agonist or antagonist.     

Steric control of conformation in self-assembly metallacalix[4]arenes derived from AlMe3 or GaMe3 with benzimidazolyl ligands

Metallacalix[4]arenes [bzimAlMe(2)](4) (1), [bzimGaMe(2)](4) (2), [mbzimAlMe(2)](4) (3) and [mbzimGaMe(2)](4) (4) were obtained by self-assembly. The larger cavity of 3 and 4 allows them to function as hosts of benzene molecules.     

Effectiveness of Physical Therapy in Patients with Tension-type Headache: Literature Review

Background: Tension-type headache (TTH) is a disease with a great incidence on quality of life and with a significant socioeconomic impact. Objectives: The aim of this review is to determine the effectiveness of physical therapy by using manual therapy (MT) for the relief of TTH. Data sources: A review was done identifying randomized controlled trials through searches in MEDLINE, PEDro, Cochrane and CINAHL (January 2002 – April 2012). Study selection: English-language studies, with adult patients and number of subjects not under 11, diagnosed with episodic tension-type headache (ETTH) and chronic tension-type headache (CTTH) were included. Data extraction: Initial search was undertaken with the words Effectiveness, Tension-type headache, and Manual therapy (39 studies). In addition, a search which included terms related to treatments such as physiotherapy, physical therapy, spinal manipulation was performed (25 studies). Results: From the two searches 9 studies met the inclusion criteria and were analysed finding statistically significant results: 1) myofascial release, cervical traction, neck muscles trigger points in cervical thoracic muscles and stretching; 2) Superficial heat and massage, connective tissue manipulation and vertebral Cyriax mobilization; 3) cervical or thoracic spinal manipulation and cervical chin-occipital manual traction; 4) massage, progressive relaxation and gentle stretching, program of active exercises of shoulder, neck and pericranial muscles; 5) massage, passive rhythmic mobilization techniques, cervical, thoracic and lumbopelvic postural correction and cranio-cervical exercises; 6) progressive muscular relaxation combined with joint mobilization, functional, muscle energy, and strain/counterstrain techniques, and cranial osteopathic treatment; 7) massage focused on relieving myofascial trigger point activity; 8) pressure release and muscle energy in suboccipital muscles; 9) combination of mobilizations of the cervical and thoracic spine, exercises and postural correction. All studies used a combination of different techniques and none analyzed treatments separately, also all the studies have assessed aspects related to TTH beyond frequency and intensity of pain. Conclusions: The findings from these studies showed evidence that physiotherapy with articulatory MT, combined with cervical muscle stretching and massage are effective for this disease in different aspects related with TTH. No evidence was found of the effectiveness of the techniques applied separately.     

Entropy dissipative one‐leg multistep time approximations of nonlinear diffusive equations

New one‐leg multistep time discretizations of nonlinear evolution equations are investigated. The main features of the scheme are the preservation of the non‐negativity and the entropy dissipation structure of the diffusive equations. The key ideas are to combine Dahlquist's G‐stability theory with entropy dissipation methods and to introduce a nonlinear transformation of variables, which provides a quadratic structure in the equations. It is shown that G‐stability of the one‐leg scheme is sufficient to derive discrete entropy dissipation estimates. The general result is applied to a cross‐diffusion system from population dynamics and a nonlinear fourth‐order quantum diffusion model, for which the existence of semidiscrete weak solutions is proved. Under some assumptions on the operator of the evolution equation, the second‐order convergence of solutions is shown. Moreover, some numerical experiments for the population model are presented, which underline the theoretical results. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 1119–1149, 2015     

Finite‐volume scheme for a degenerate cross‐diffusion model motivated from ion transport

An implicit Euler finite‐volume scheme for a degenerate cross‐diffusion system describing the ion transport through biological membranes is proposed. The strongly coupled equations for the ion concentrations include drift terms involving the electric potential, which is coupled to the concentrations through the Poisson equation. The cross‐diffusion system possesses a formal gradient‐flow structure revealing nonstandard degeneracies, which lead to considerable mathematical difficulties. The finite‐volume scheme is based on two‐point flux approximations with “double” upwind mobilities. The existence of solutions to the fully discrete scheme is proved. When the particles are not distinguishable and the dynamics is driven by cross diffusion only, it is shown that the scheme preserves the structure of the equations like nonnegativity, upper bounds, and entropy dissipation. The degeneracy is overcome by proving a new discrete Aubin–Lions lemma of “degenerate” type. Numerical simulations of a calcium‐selective ion channel in two space dimensions show that the scheme is efficient even in the general case of ion transport.     

Dielectric relaxation in bulk and cylindrically confined octylcyanobiphenyl (8CB)

The dielectric relaxation spectrum over the frequency range 10² to 1.8×10⁹ Hz of 4‐octyl‐4′‐cyanobiphenyl, 8CB, in bulk and confined to 200 nm diameter cylindrical pores is reported. We used matrices with parallel cylindrical pores, obtaining different alignments of the molecular director depending on the treatment. Results show that there are two relaxations in the isotropic phase and in the mesophases for parallel alignment and three for perpendicular alignment. The molecular origin of theses modes and the effect of the confinement on their dynamics are discussed. To compare properly the results for bulk and confined 8CB, a re‐scaling of the experimental data is proposed.