Experimental and theoretical Raman and surface‐enhanced Raman scattering study of cysteine

Raman spectra in solid and 1 M solution of L ‐cysteine and surface‐enhanced Raman scattering (SERS) spectra of this molecule in the zwitterionic form, by using colloidal silver nanoparticles, have been recorded. Density functional theory with the B3LYP functional was used for the optimizations of the ground state geometries and simulation of the vibrational spectrum of this amino acid. The SERS spectrum with a large silver cluster as a model metallic surface was simulated for the first time. Taking into account the experimental and calculated Raman and SERS vibrations and the corresponding assignments, as well as a comparison of force constants and geometrical parameters between the free zwitterion cysteine and the one in the presence of the colloidal silver nanoparticles, we can confirm the presence of gauche (P_H) and trans (P_N) rotamers in the solid state, the formation of a S S bond in the solution state, the dissociation of the peptide bond and mixing of rotamers because of the SERS effect, and the relative importance of the interaction of sulphyldryl, NH₃⁺, and carboxylate groups with the metallic surface. Copyright © 2009 John Wiley & Sons, Ltd.     

A modification of the Social Force Model can reproduce experimental data of pedestrian flows in normal conditions

The Social Force Model presents some limitations when describing the experimental data of pedestrian flows in normal conditions — in particular the specific flow rates for different door widths and the fundamental diagram.In the present work we propose a modification of this model that consists of a self-stopping mechanism to prevent a simulated pedestrian from continuously pushing over other pedestrians.With this simple change, the modified model is able to reproduce the specific flow rates and fundamental diagram of pedestrian flows for normal conditions, as reported in the literature.     

Determination of Rare Earth Elements in Natural Water Samples by Rapid Sequential High-Resolution Continuum Source Flame Atomic Absorption Spectrometry (HR CS FAAS) and inductively Coupled Plasma-Mass Spectrometry (ICP-MS)

A method was developed to sequentially assay ten rare earth elements by high-resolution continuum source flame atomic absorption spectrometry. The rare earth elements Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, Y, and Sc were assayed in environmental water samples which were also analyzed by a reference inductively coupled plasma-mass spectrometry protocol. The samples did not require pretreatment or preconcentration. Interferences for the method were evaluated. Experimental parameters, including the flame composition, burner height, ionization buffers and number of pixels, were optimized. The volume necessary to run measurements in triplicate was only 15?mL per sample. The accuracy, precision and linear range were evaluated. The limits of detection ranged from 0.003 to 0.473?µg mL^?1 for the most sensitive (Yb) to the least sensitive (Tb) element.     

Why monotonous and non-monotonous steady-flow curves can be obtained with the same non-Newtonian fluid? A single explanation

We show that a pronounced variation of the apparent viscosity with shear joined to the control shear mode of a rheometer can justify why monotonous and non-monotonous steady-flow curves can be obtained testing the same non-Newtonian fluid.     

Classical Limit and Quantum Logic

The analysis of the classical limit of quantum mechanics usually focuses on the state of the system. The general idea is to explain the disappearance of the interference terms of quantum states appealing to the decoherence process induced by the environment. However, in these approaches it is not explained how the structure of quantum properties becomes classical. In this paper, we consider the classical limit from a different perspective. We consider the set of properties of a quantum system and we study the quantum-to-classical transition of its logical structure. The aim is to open the door to a new study based on dynamical logics, that is, logics that change over time. In particular, we appeal to the notion of hybrid logics to describe semiclassical systems. Moreover, we consider systems with many characteristic decoherence times, whose sublattices of properties become distributive at different times.     

Existence of solution for a nonvariational elliptic system with exponential growth in dimension two

We prove existence of solution for an elliptic system on a bounded domain in dimension two. We use the Galerkin scheme in the product of Hilbert spaces. The nonlinearities may have subcritical or critical exponential growth.     

Igusa–Todorov functions for Artin algebras

In this paper we study the behavior of the Igusa–Todorov functions for Artin algebras A with finite injective dimension, and Gorenstein algebras as a particular case. We show that the ?-dimension and ψ-dimension are finite in both cases. Also we prove that monomial, gentle and cluster tilted algebras have finite ?-dimension and finite ψ-dimension.     

Biodegradable polymer/clay systems for highly controlled release of NPK fertilizer

The aim of this work was to obtain biodegradable polymeric systems based on poly(hydroxybutyrate) (PHB) for use in the controlled release of agrochemicals and to analyze the relationship between the properties of polymers and the rates of release of active compounds. Two types of systems were obtained: one using nitrogen, phosphorous, and potassium (NPK) fertilizer directly mixed within the polymer matrix and another with the fertilizer previously incorporated in bentonite (Bent) and mixed with the polymer. The systems were obtained by melt processing and then evaluated by their properties. The release of the active compounds was analyzed by conductometric analysis using an aqueous solution as release medium for 240 hours. The obtained results were correlated with the biodegradation process of PHB. All of the systems presented a significant reduction in the active compounds released to the environment as compared with the direct application of NPK. The PHB/NPK systems showed a release of up to 37% of the compounds, while the PHB/m‐Bent showed greater control, with a release between 4% and 11% after 240 hours. In addition, the properties of the polymer systems presented a direct relationship with the rate of active compounds released. The type of production process, properties, and biodegradability indicate interesting potential of these systems for application in the controlled release of active compounds.     

Characterization of Brain Metabolism by Nuclear Magnetic Resonance

The noninvasive, quantitative ability of nuclear magnetic resonance (NMR) spectroscopy to characterize small molecule metabolites has long been recognized as a major strength of its application in biology. Numerous techniques exist for characterizing metabolism in living, excised, or extracted tissue, with a particular focus on ¹H-based methods due to the high sensitivity and natural abundance of protons. With the increasing use of high magnetic fields, the utility of in vivo ¹H magnetic resonance spectroscopy (MRS) has markedly improved for measuring specific metabolite concentrations in biological tissues. Higher fields, coupled with recent developments in hyperpolarization, also enable techniques for complimenting ¹H measurements with spectroscopy of other nuclei, such as ³¹P and ¹³C, and for combining measurements of metabolite pools with metabolic flux measurements. We compare ex vivo and in vivo methods for studying metabolism in the brain using NMR and highlight insights gained through using higher magnetic fields, the advent of dissolution dynamic nuclear polarization, and combining in vivo MRS and ex vivo NMR approaches.     

Citation for the 2003 ICMI Felix Klein medal to Guy Brousseau

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Citation for the 2003 ICMI Felix Klein medal to Guy Brousseau