Self-force on an electric dipole in the spacetime of a cosmic string

We calculate the electrostatic self-force on an electric dipole in the spacetime generated by a static, thin, infinite and straight cosmic string. The electric dipole is held fixed in different configurations, namely, parallel, perpendicular to the cosmic string and oriented along the azimuthal direction around this topological defect, which is stretched along the z$z$ axis. We show that the self-force is equivalent to an interaction of the electric dipole with an effective dipole moment which depends on the linear mass density of the cosmic string and on the configuration. The plots of the self-forces as functions of the parameter which determines the angular deficit of the cosmic string are shown for those different configurations.     

Polyelectrolyte complexes of chitosan/heparin and <Emphasis Type="Italic">N,N,N-</Emphasis>trimethyl chitosan/heparin obtained at different pH: I. Preparation,characterization, and controlled release of heparin

Chitosan and N,N,N-trimethyl chitosan (TMC) were treated with heparin (HP) to produce polyelectrolyte complexes (PECs). The structures of PECs were characterized by Fourier transform infrared and CP-MAS ¹³C NMR spectroscopies. A thermal stability of TMC/HP complex was evaluated by thermogravimetric analyses, and morphology was investigated by SEM images. The ratio between the carbons bonded to noncharged nitrogen atoms (CΦ) and the carbons bonded to positively charged nitrogen atoms (Cω) in TMC was calculated through of the degree quaternization (DQ), being the DQ obtained through ¹H NMR data. Experiments of controlled release of HP were performed in distilled water at pH ∼7, using methylene blue/heparin system as solute. The release profiles of HP from TMC/HP complex are quite different each other. The value of CΦ/Cω ratio was used for explaining such an effect. The CΦ/Cω ratio tends to be constantly (∼0.69) as high as the pH of medium in which the PEC of TMC/HP was obtained. The change of CΦ/Cω ratio on the pH was also considered to explain the improvement of thermal stability of PEC2 with increase of pH. Data show that PEC of TMC/HP formed at pH 8 is a promising material for uses in oral site-specific HP release systems.     

Simple and rapid CE-UV method for the assessment of trail pheromone compounds of leaf-cutting ants' venom glands

Leaf-cutting ants cause large losses in several crops around the world. In the ant species Atta sexdens, each colony comprises up to 5 million individuals. In order to keep a close connection among such a large number of individuals, an efficient chemical communication system is necessary. Among other different substances, these animals use alkylpyrazines to mark their trails and to guide ant workers from the nest to their sources of food. In this study, CE-UV was used to apply a method for qualitative analysis of venom gland components of leaf-cutting ants. Mobility of these compounds proved to be a function of the ionization capability of these bases as well as their volumes. Migration order was thoroughly explained in terms of such parameters. The best analysis conditions were achieved with a BGE composed by 0.8% formic acid plus 20% methanol in water, hydrodynamic injection, and application of external pressure. Such analysis conditions may be easily applied in CE-MS analyses as well. CE-UV analyses proved to be as adequate as GC to analyze such compounds due to system detectability (LD ? 0.005?mmol/L), separation efficiency (from 5.07×10(4) to 1.23×10(5) theoretical plates), and resolution (minimum of 2.35). In addition, analysis time was ca. 15 min, which shows another advantage of CE analysis when compared with GC. Although the analytes are found in concentrations as low as 50 ng/venom glands, four putative pyrazine ring moiety substances could be detected in real samples, due to sample stacking and use of a capillary with extended detection cell.     

Surface‐enhanced Raman micro‐spectroscopy of DNA/RNA bases adsorbed on pyroxene rocks as a test of in situ search for life traces on Mars

SERS spectroscopy with 785‐nm laser excitation minimizing fluorescence emission is exploited for remote analysis of life traces in an extraterrestrial environment. Adenine and guanine, nucleobases present in both DNA and RNA strands, and microRNA containing adenine and guanine have been used as testing ligands for identifying traces of nucleic acids in Martian rocks and sediments. SERS spectra of these nucleobase samples adsorbed on pyroxene substrates have been investigated with micro‐Raman apparatus in the absence of sample manipulation and inducing the signal enhancement by deposition of silver colloidal nanoparticles over the pyroxene/nucleobase substrates. An order‐of‐magnitude estimate of the sample amount responsible for the SERS spectra is given. Copyright © 2009 John Wiley & Sons, Ltd.