Fiber orientation kinetics of a concentrated short glass fiber suspension in startup of simple shear flow

The common approach for simulating the evolution of fiber orientation during flow in concentrated suspensions is to use an empirically modified form of Jeffery's equation referred to as the Folgar–Tucker (F-T) model. Direct measurements of fiber orientation were performed in the startup of shear flow for a 30 wt% short glass fiber-filled polybutylene terephthalate (PBT-30); a matrix that behaves similar to a Newtonian fluid. Comparison between predictions based on the F-T model and the experimental fiber orientation show that the model over predicts the rate of fiber reorientation. Rheological measurements of the stress growth functions show that the stress overshoot phenomenon approaches a steady state at a similar strain as the fiber microstructure, at roughly 50 units. However, fiber orientation measurements suggest that a steady state is not reached as the fiber orientation continues to slowly evolve, even up to 200 strain units. The addition of a “slip” parameter to the F-T model improved the model predictions of the fiber orientation and rheological stress growth functions.     

Ammonium perfluorooctanoate as a volatile surfactant for the analysis of N-methylcarbamates by MEKC-ESI-MS

Ammonium perfluorooctanoate (APFOA) was investigated as an MS-friendly surfactant for the analysis of a mixture of ten N-methylcarbamates with MEKC-ESI-MS. Because of the relatively low boiling point of perfluorooctanoic acid ( approximately 190 degrees C), APFOA can be introduced into a mass spectrometer without the adverse effects of less volatile surfactants such as SDS. With a BGE consisting of 50 mM APFOA/isopropanol (IPA) 98:2 and with 30 kV applied, a very fast separation ( approximately 6 min) was possible with only one pair of analytes comigrating. Using an experimental design with four factors (voltage, nebulizer pressure, concentration of APFOA, and concentration of IPA) we were able to resolve all analytes in just over 11 min. Sheath liquid composition and flow rate, drying gas temperature and flow rate, and fragmentor voltage were then optimized for maximum signal intensity and S/N. It was found that the faster method gave better S/N because of narrower peak widths, and detection limits in SIM mode were between 0.01 (aldicarb) and 0.08 mg/L (methomyl). Calibration curves were prepared with standards of 0.50, 1.00, and 2.00 mg/L for the analysis of samples obtained after SPE of tap water spiked with the ten N-methylcarbamates at a level of 10 microg/L. All analytes showed very good recoveries (>86%), except for the most polar analyte aldicarb sulfone (recovery of 73%), testifying for the potential use of APFOA for this kind of analyses.     

HPLC-UV and HPLC-MSn multiresidue determination of amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl and azoxystrobin in surface waters

The paper presents a new HPLC method, with UV and MSⁿ detection, for the determination of seven pesticides, including the sulfonylurea herbicides amidosulfuron, azimsulfuron, nicosulfuron, rimsulfuron, thifensulfuron methyl, tribenuron methyl, and the fungicide azoxystrobin characterised by a methoxyacrilate structure. The methodology consists of a preconcentration/SPE (solid phase extraction) step and HPLC-UV (240 nm detection wavelength)-MSⁿ analysis. Under the optimised conditions and after a 1000/1 preconcentration factor, the limits of detection were lower than 14.5 ng L⁻¹ for UV detection and lower than 8.1 ng L⁻¹ for MS detection. The limits of quantification were lower than 48.3 ng L⁻¹ in UV detection and than 26.9 ng L⁻¹ in MSⁿ detection. The analysis of two samples, spiked with a mixture of the pesticides at threshold level concentrations, gave more than 60% recovery.     

Palladium(II) and platinum(II) organometallic complexes with the model nucleobase anions of thymine, uracil, and cytosine: antitumor activity and interactions with DNA of the platinum compounds

Pd(II) and Pt(II) complexes with the anions of the model nucleobases 1-methylthymine (1-MethyH), 1-methyluracil (1-MeuraH), and 1-methylcytosine (1-MecytH) of the types [Pd(dmba)(mu-L)]2 [dmba = N,C-chelating 2-((dimethylamino)methyl)phenyl; L = 1-Methy, 1-Meura or 1-Mecyt] and [M(dmba)(L)(L')] [L = 1-Methy or 1-Meura; L' = PPh(3) (M = Pd or Pt), DMSO (M = Pt)] have been obtained. Palladium complexes of the types [Pd(C6F5)(N-N)(L)] [L = 1-Methy or 1-Meura; N-N = N,N,N',N'-tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), or 4,4'-dimethyl-2,2'-bipyridine (Me2bpy)] and [NBu4][Pd(C6F5)(1-Methy)2(H2O)] have also been prepared. The crystal structures of [Pd(dmba)(mu-1-Methy)]2, [Pd(dmba)(mu-1-Mecyt)]2.2CHCl3, [Pd(dmba)(1-Methy)(PPh3)].3CHCl3, [Pt(dmba)(1-Methy)(PPh3)], [Pd(tmeda)(C6F5)(1-Methy)], and [NBu4][Pd(C6F5)(1-Methy)2(H2O)].H2O have been established by X-ray diffraction. The DNA adduct formation of the new platinum complexes synthesized was followed by circular dichroism and electrophoretic mobility. Atomic force microscopy images of the modifications caused by the platinum complexes on plasmid DNA pBR322 were also obtained. Values of IC50 were also calculated for the new platinum complexes against the tumor cell line HL-60. All the new platinum complexes were more active than cisplatin (up to 20-fold in some cases).     

Deformations of Functions and F-Manifolds

We study deformations of functions on isolated singularities.A unified proof of the equality of Milnor and Tjurina numbersfor functions on isolated complete intersections singularitiesand space curves is given. As a consequence, the base spaceof their miniversal deformations is endowed with the structureof an F-manifold, and we can prove a conjecture of V. Goryunov,stating that the critical values of the miniversal unfoldingof a function on a space curve are generically local coordinateson the base space of the deformation. 2000 Mathematics SubjectClassification 32S05.     

Quantization of bending flows

We briefly review the Kapovich-Millson notion of bending flows as an integrable system on the space of polygons inR ³, its connection with a specific GaudinXXX system, as well as the generalization to su(r),r>2. Then we consider the quantization problem of the set of Hamiltonians pertaining to the problem, quite naturally called bending Hamiltonians, and prove that their commutativity is preserved at the quantum level.     

Reversible intercalation of ammonia molecules into a layered double hydroxide structure without exchanging nitrate counter-ions

A zinc/aluminum LDH was precipitated with recycled ammonia from a chemical vapor deposition reaction. The LDH presented a crystalline phase with basal distance of 8.9 Å, typical for nitrate-containing LDHs, and another phase with a basal distance of 13.9 Å. Thermal treatment at 150 °C eliminated the phase with the bigger basal distance leaving only the anhydrous nitrate-intercalated LDH structure with 8.9 Å. Intense N-H stretching modes in the FTIR spectra suggested that the expansion was due to intercalation of ammonia in the form of [NH₄(NH₃)_n]⁺ species. When additional samples were precipitated with pure ammonia, the conventional LDH nitrate structure was obtained (8.9 Å basal distance) at pH=7, as well as a pure crystalline phase with 13.9 Å basal distance at pH=10 due to ammonia intercalation that can be removed by heating at 150 °C or by stirring in acetone, confirming a unusual sensu stricto intercalation process into a LDH without exchanging nitrate ions.     

Solar UV irradiation conditions on the surface of Mars

The UV radiation environment on planetary surfaces and within atmospheres is of importance in a wide range of scientific disciplines. Solar UV radiation is a driving force of chemical and organic evolution and serves also as a constraint in biological evolution. In this work we modeled the transmission of present and early solar UV radiation from 200 to 400 nm through the present-day and early (3.5 Gyr ago) Martian atmosphere for a variety of possible cases, including dust loading, observed and modeled O3 concentrations. The UV stress on microorganisms and/or molecules essential for life was estimated by using DNA damaging effects (specifically bacteriophage T7 killing and uracil dimerization) for various irradiation conditions on the present and ancient Martian surface. Our study suggests that the UV irradiance on the early Martian surface 3.5 Gyr ago may have been comparable with that of present-day Earth, and though the current Martian UV environment is still quite severe from a biological viewpoint, we show that substantial protection can still be afforded under dust and ice.