Oxygen evolution on well-characterized mass-selected Ru and RuO2 nanoparticles

Oxygen evolution was investigated on model, mass-selected RuO₂ nanoparticles in acid, prepared by magnetron sputtering. Our investigations include electrochemical measurements, electron microscopy, scanning tunneling microscopy and X-ray photoelectron spectroscopy. We show that the stability and activity of nanoparticulate RuO₂ is highly sensitive to its surface pretreatment. At 0.25 V overpotential, the catalysts show a mass activity of up to 0.6 A mg^–1 and a turnover frequency of 0.65 s^–1, one order of magnitude higher than the current state-of-the-art.     

Low intensity infrared laser induces filamentation in Escherichia coli cells

Laser Physics - Low intensity continuous wave and pulsed emission modes laser is used in treating many diseases and the resulting biostimulative effect on tissues has been described, yet the...     

Poly(ethylene oxide-co-epichlorohydrin)/NaI: a promising polymer electrolyte for photoelectrochemical cells

We have investigated the thermal and ionic conductivity properties of the elastomer poly(ethylene oxide-co-epichlorohydrin) filled with NaI and I₂. The reason for using this composition is its potential application as electrolyte in photoelectrochemical cells. This copolymer was characterized as a function of NaI concentration, temperature and relative humidity. According to the data obtained, the Na⁺ ion interacts with the ethylene oxide repeating units by means of Lewis type acid–base interactions. The empirical Vogel–Tamman–Fulcher equation was used to model the conductivity and temperature relationships, indicating that the conduction occurs in the amorphous phase of the copolymer. The sample with 9.0% (w/w) of NaI presents a conductivity of 1.5×10⁻⁵ S cm⁻¹ in a dry atmosphere (30°C, [H₂O]<1 ppm) and 2.0×10⁻⁴ S cm⁻¹ at 86% relative humidity (22°C).     

A proximal-like method for a class of second order measure-differential inclusions describing vibro-impact problems

We are interested in the study of discrete mechanical systems subjected to frictionless unilateral constraints. The dynamics is described by a second order measure-differential inclusion for the unknown positions, completed by a Newton's impact law describing the transmission of the velocities when the constraints are saturated.By using another formulation of the problem at the velocity level, we introduce a time-stepping algorithm, inspired by the proximal methods for differential inclusions, and we prove the convergence of the approximate solutions to a solution of the Cauchy problem.     

The importance of the mixed phase in hybrid stars built with the Nambu-Jona-Lasinio model

We investigate the structure of hybrid stars based on two different constructions: one is based on the Gibbs condition for phase coexistence and considers the existence of a mixed phase (MP), and the other is based on the Maxwell construction and no mixed phase is obtained. The hadron phase is described by the non-linear Walecka model (NLW) and the quark phase by the Nambu-Jona-Lasinio model (NJL). We conclude that the masses and radii obtained are model dependent but not significantly different for both constructions.     

Synthesis, basicity, structural characterization, and biochemical properties of two [(3-hydroxy-4-pyron-2-yl)methyl]amine derivatives showing antineoplastic features

The N,N'-bis[(3-hydroxy-4-pyron-2-yl)methyl]-N,N'-dimethylethylendiamine (malten) and 4,10-bis[(3-hydroxy-4-pyron-2-yl)methyl]-1,7-dimethyl-1,4,7,10-tetraazacyclododecane (maltonis) were synthesized and characterized. The acid-base behavior, structural characterizations, and biochemical studies in aqueous solution were reported. Each compound contains two 3-hydroxy-2-methyl-4-pyrone units (maltol) symmetrically spaced by a polyamine fragment, the 1,4-dimethylethylendiamine (malten), or the 1,7-dimethyl-1,4,7,10-tetraazacyclododecane (maltonis). They are present at physiological pH 7.4 in the form of differently charged species: neutral but in a zwitterion form for malten and monopositive with an internal separation of charges for maltonis. Malten and maltonis are both able to alter the chromatin structure inducing the covalent binding of genomic DNA with proteins, a feature consistent with the known antiproliferative activity exerted by this class of molecules. Solid-state results and MD simulations in water show that malten, because of its molecular topology, should be more prone than maltonis to act as a donor of H-bonds in intermolecular contacts, thus it should give a better noncovalent approach with the negatively charged DNA. Crystal structures of [H(2)malten](2+) and [H(2)maltonis](2+) cations were also reported.     

A method for correcting standard-based real-time PCR DNA quantitation when the standard’s polymerase reaction efficiency is significantly different from that of the unknown’s

Standard-based real-time or quantitative polymerase chain reaction quantitation of an unknown sample’s DNA concentration (i.e., [DNA]_unk) assumes that the concentration dependence of the standard and unknown reactions (related to reaction efficiency, E) are equivalent. In our work with background food-borne organisms which can interfere with pathogen detection, we have found that it is generally possible to achieve an acceptable E (1 ± 0.05) for standard solutions by optimizing the PCR conditions, template purity, primer sequence, and amplicon lengths. However, this is frequently not true for the solutions containing unknown amounts of target DNA inasmuch as cell extracts are more chemically complex than the standards which have been amplified (2³⁰-fold) as well as undergone a purification process. When significant differences in E occur, it is not possible to accurately estimate unknown target DNA concentration from the standard solution’s slope and intercept (from threshold cycle number, or C _T , versus Log[DNA] data). What is needed is a standard-mediated intercept which can be specifically coupled with an unknown solution’s PCR concentration dependence. In this work, we develop a simple mathematical procedure to generate a new standard curve with a slope (∂C _T /∂Log[Dilution]_unk) derived from at least three dilutions of the unknown target DNA solution ([DNA]_unk) and an intercept calculated from the unknown’s C _T  s, DNA concentrations interpolated from the standard curve (i.e., the traditional estimate of [DNA]_unk), and ∂C _T /∂Log[Dilution]_unk. We were able to achieve this due to our discovery of the predictable way in which the observed and ideal C _T versus Log[DNA] slopes and intercepts deviate from one another. This “correction” in the standard-based [DNA]_unk determination is typically 20–60% when the difference in the standard and unknown E is >0.1.     

Semistrict models of connected 3-types and Tamsamani’s weak 3-groupoids

Homotopy 3-types can be modelled algebraically by Tamsamani’s weak 3-groupoids as well as, in the path-connected case, by cat²-groups. This paper gives a comparison between the two models in the path-connected case. This leads to two different semistrict algebraic models of connected 3-types using Tamsamani’s model. Both are then related to Gray groupoids.     

A rapid method for the detection of foodborne pathogens by extraction of a trace amount of DNA from raw milk based on amino-modified silica-coated magnetic nanoparticles and polymerase chain reaction

A method based on amino-modified silica-coated magnetic nanoparticles (ASMNPs) and polymerase chain reaction (PCR) was developed to rapidly and sensitively detect foodborne pathogens in raw milk. After optimizing parameters such as pH, temperature, and time, a trace amount of genomic DNA of pathogens could be extracted directly from complex matrices such as raw milk using ASMNPs. The magnetically separated complexes of genomic DNA and ASMNPs were directly subjected to single PCR (S-PCR) or multiplex PCR (M-PCR) to detect single or multiple pathogens from raw milk samples. Salmonella Enteritidis (Gram-negative) and Listeria monocytogenes (Gram-positive) were used as model organisms to artificially contaminate raw milk samples. After magnetic separation and S-PCR, the detection sensitivities were 8 CFU mL⁻¹ and 13 CFU mL⁻¹ respectively for these two types of pathogens. Furthermore, this method was successfully used to detect multiple pathogens (S. Enteritidis and L. monocytogenes) from artificially contaminated raw milk using M-PCR at sensitivities of 15 CFU mL⁻¹ and 25 CFU mL⁻¹, respectively. This method has great potential to rapidly and sensitively detect pathogens in raw milk or other complex food matrices.     

Electrosynthesis and characterization of poly(3-methylthiophene) on different substrates

 We report on the study of the electropolymerization of 3-methylthiophene onto Pt, p-Si and indium-tin oxide deposited on polyester using quartz crystal microgravimetry, electrochemical and spectroelectrochemical measurements. We observe that potential variation during the galvanostatic electrodeposition is correlated with the nucleation process. The mass variation of poly(3-methylthiophene) is linear with the amount of the electrochemical charge whereas the absorbance variation curve shows two distinct slopes. The latter result has been explained in terms of conjugation length variation during polymer growth. Scanning electron microscopy analysis allowed the detection of morphological changes from a dense and compact structure to an open morphology when the poly(3-methylthiophene) film thickness increases. The roughness of the films did not change considerably with the substrate, as observed by atomic force microscopy. Absorption and photocurrent spectra at different film thicknesses show a shift of the peaks to lower wavelengths when the thickness increased, thus confirming the decrease of mean conjugation length in thicker films. Received: 1 September 1998 / Accepted: 11 November 1998