A Simple and Validated LC Method for the Simultaneous Determination of Three Compounds in Mikania laevigata Extracts

The Mikania genus is widely known as guaco and is used to treat fever, rheumatism, influenza and respiratory diseases. This article deals with the simultaneous quantification of three commercially available phenolic markers (o-coumaric acid, coumarin and syringaldehyde) in M. laevigata extracts, through LC-PDA. The validation data show that the method is specific, accurate, precise and robust, and also indicative of the stability of guaco extract. The method was linear, over a range of 1.25–20.0 μg mL⁻¹ for o-coumaric acid, 2.5–40.0 μg mL⁻¹ for coumarin, and 0.25–4.0 μg mL⁻¹ for syringaldehyde. The range of recovery was 94.3–96.4% for all the components, at a level of 100%.

     

Methylmercury determination using a hyphenated high performance liquid chromatography ultraviolet cold vapor multipath atomic absorption spectrometry system

The present work investigates the use of a multipath cell atomic absorption mercury detector for mercury speciation analysis in a hyphenated high performance liquid chromatography assembly. The multipath absorption cell multiplies the optical path while energy losses are compensated by a very intense primary source. Zeeman-effect background correction compensates for non-specific absorption. For the separation step, the mobile phase consisted in a 0.010% m/v mercaptoethanol solution in 5% methanol (pH = 5), a C₁₈ column was used as stationary phase, and post column treatment was performed by UV irradiation (60 °C, 13 W). The eluate was then merged with 3 mol L^− 1 HCl, reduction was performed by a NaBH₄ solution, and the Hg vapor formed was separated at the gas–liquid separator and carried through a desiccant membrane to the detector. The detector was easily attached to the system, since an external gas flow to the gas–liquid separator was provided. A multivariate approach was used to optimize the procedure and peak area was used for measurement. Instrumental limits of detection of 0.05 µg L^− 1 were obtained for ionic (Hg²⁺) and HgCH₃⁺, for an injection volume of 200 µL. The multipath atomic absorption spectrometer proved to be a competitive mercury detector in hyphenated systems in relation to the most commonly used atomic fluorescence and inductively coupled plasma mass spectrometric detectors. Preliminary application studies were performed for the determination of methyl mercury in sediments.     

Highly structured duets in the song of the South American Hornero

The South American Hornero (Furnarius rufus) is a suboscine bird widely known for its mud-made, oven-looking nest. Beyond their architectural skills, the male and female Horneros sing in highly structured duets. The analysis of field recordings reported in this work reveals that as the male increases the note production rate the female responds by switching to different locking states: the ones predicted by the theory of nonlinear forced oscillators. This gives the duet a most appealing rhythm, and unveils the nonlinear nature of the underlying brain activity needed to generate the song.     

Multiparticle production in proton-nucleus collisions at 360 GeV/c using the European Hybrid spectrometer

360 GeV/c proton interactions with aluminium (Al) and gold (Au) targets are studied using the European Hybrid Spectrometer (EHS) equipped with the Rapid Cycling Bubble Chamber (RCBC). Multiplicities, rapidity distributions and correlations between leading and other produced particles are presented and compared with Monte Carlo calculations based on the multi-chain and Lund models.     

Topological cross sections and charged particle multiplicities inpp interactions at 360 GeV/c

Using data obtained with EHS equipped with the Rapid Cycling Bubble Chamber (RCBC) exposed to a proton beam of 360 GeV/c, we calculate topological cross sections. We present in great detail the procedure and the techniques used to correct raw data. Finally, we give multiplicity moments and multiplicity correlations and we compare the values obtained in our experiment, together with data at other energies, with different models.     

ANALYSIS OF A LIMPET FISHERY USING A METAPHYSIOLOGICAL STAND-GROWTH MODEL

We use a metaphysiological approach, recently proposed by one of us (WMG), for modeling trophic interactions to develop a model of limpet-algae-kelp dynamics using data obtained by the others (RHB and GMB) from studies along the west coast of South Africa. We test whether the model is able to predict limpet population growth reasonably well in both the presence and absence of kelp and over a range of limpet and algal population densities. We then discuss the development of a limpet fishery, suing the model to predict limpet stand growth under various harvesting regimes. We compare our results to those obtained by others using a classical size-structured approach, and we suggest how both approaches can be combined to obtain a more reliable and applicable model than either on its own.     

The cation-π cloud interaction and the zeolite basicity concept

Two adsorption complexes between pyrrole and alkaline T₆ zeolite clusters were studied theoretically using DFT method. Results show that at B3LYP/6-311+G**//B3LYP/6-31G* the oxygen atoms in LiT₆ are, in average, more charged than in CsT₆. The cation-π complex is more stable than the complex possessing a hydrogen bond between T₆ clusters and pyrrole. Correlations between alkaline cation hardness and ΔH_adsorption (kcal/mol) showed a linear correlation for both complexes, indicating that the driving force for pyrrole adsorption is cation hardness.     

Real-time three-dimensional optical micromanipulation of multiple particles and living cells

Counterpropagating light fields provide a stationary optical potential well for a Brownian particle. Introducing variability in the relative strengths of the counterpropagating beams allows us to create a more general configuration-the optical elevator. An optical elevator dynamically controls the axial location of the potential minimum where the particle finds a stable equilibrium position. We describe the implementation of multiple real-time reconfigurable optical elevators with the generalized phase contrast method for dynamic manipulation of polystyrene spheres and yeast cells S. cerevisiae in three dimensions.