Determination of carbon in natural freshwater biofilms with total reflection X-ray fluorescence spectrometry

There is a growing interest in determination of low Z elements, i.e., carbon to phosphorus, in biological samples. Total reflection X-ray fluorescence spectrometry (TXRF) has been already established as suitable trace element analytical method with low sample demand and quite good quantification limits. Recently, the determinable element range was extended towards Z = 6 (carbon).Biofilms can be used for biomonioring purposes in the aquatic environment. Besides the trace metals, especially the determination of the carbon content is important for the better understanding of the early stage of biofilm formation. For this, an ATI low Z spectrometer equipped with Cr-anode X-ray tube, multilayer monochromator, vacuum chamber, and a Si(Li) detector with ultra thin window was used. Biofilms were grown on two different artificial supports (granite and plexiglass), freeze dried, suspended in high purity water and analyzed. As an internal standard the natural titanium content of the biofilms was used. The accuracy of the method was checked by total carbon measurement using a combusting carbon analyzer.     

Synthesis of the new pyrido[1,2-c]benzo-v-triazinium system via valence bond isomerization

α-Pyridylphenyl diazonium salts 2 were found to undergo valence bond isomerization and gave the new pyrido[ 1 ,2-c]benzo-v-triazinium salts 3. The ir and nmr studies on the products showed that isomers 2 and 3 form an equilibrium, and the ring closure is favoured by electron withdrawing substituents.     

Separation of anti-tumor peptides by capillary electrophoresis in organic solvent containing background electrolytes

Connections between the calculated and measured electrophoretic mobilities (nu(ep)) determined by capillary electrophoresis as well as connections between the measured and calculated diffusion coefficients of anti-tumor peptides have been investigated in background electrolytes (BGEs) containing different organic solvents (acetonitrile, methanol, ethanol and isopropanol). Comparison of the electrophoretic mobility (nu(ep)) values revealed discrepancies between the measured and calculated values. However, no change in the migration order or selectivity could be expected from the calculated nu(ep) values, variation of both properties was observed applying organic solvents as BGE modifiers. Experimental determination of the diffusion coefficient suggested that the effect of the organic solvents is not restricted to the change of the BGE viscosity. The reason for the discrepancy between the measured and calculated mobility values might be the possible conformation and/or solvation changes of the peptide caused by the different organic solvents.     

The Prouhet–Tarry–Escott problem,indecomposability of polynomials and Diophantine equations

The Ramanujan Journal - In this paper, we show how the subjects mentioned in the title are related. First we study the structure of partitions of $$A subseteq {1, dots , n}$$ in k-sets such...     

Dynamic Shear Viscosity in a 2D Yukawa System

We present non‐equilibrium molecular dynamics simulation studies on the dynamic (complex) shear viscosity of a 2D many‐particle system interacting via a Yukawa (Debye‐Hückel) type inter‐particle potential. Our investigations reveal the complex interplay of dissipative and elastic processes, as well as the effect of single particle resonances and enhanced collective excitations, and the influence of the external forces on the structural correlations in the system (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of Dinitrogen,Methane, Carbon Monoxide,and Carbon Dioxide Mass‐Transport Dynamics in Carbon and Zeolite Molecular Sieves

Equilibrium (based on Henry constants) and kinetic (based on relaxation‐time constants or rather macropore transport diffusivities) selectivities for commercial zeolite and carbon‐molecular‐sieve (CMS) adsorbents were compared. Adsorption isotherms were recorded at ?20°. The frequency‐response (FR) sorption‐rate spectra were determined in the range of ?78 and 70° at 133 Pa. In particles of a larger size than 1.0 mm, macropore diffusion governed the rate of sorption mass transport in both types of microporous materials. The differences in the intercrystalline diffusivities established the kinetic separation of the gases notwithstanding the essential importance of interactions in the micropores. Zeolites seem to be more advantageous for a dynamic separation of CO₂ and CH₄ than CMS 4A. With the CO₂ and CO pair, the CMS is characterized by short characteristic times which, together with a good separation factor, is a double advantage in a short‐cycle adsorption technology. Upon comminution of the carbon pellets, intercrystalline‐diffusion resistance can be completely removed by using CMS 4A adsorbent particles with a diameter smaller than 1 mm. The carbonization of spruce‐wood cubes resulted in an excellent carbon honeycomb structure, which seems to be ideal from a dynamic point of view for applications in short‐cycle adsorption‐separation technologies. In the development of adsorbents, the use of the FR method can be beneficial.     

Derivation of a dual-mixed <Emphasis Type=Italic>hp</Emphasis>-finite element model for axisymmetrically loaded cylindrical shells

The two-field dual-mixed Fraeijs de Veubeke variational formulation of three-dimensional elasticity serves as the starting point of the derivation of a dimensionally reduced shell model presented in this paper. The fundamental variables of this complementary energy-based variational principle are the not a priori symmetric stress tensor and the skew-symmetric rotation tensor. The tensor of first-order stress functions is applied to satisfy translational equilibrium, while the rotation tensor plays the role of a Lagrange multiplier to ensure rotational equilibrium. The volumetric locking-free shell model uses unmodified three-dimensional constitutive equations, and no classical kinematical hypotheses are employed during the derivation. The numerical performance of the related low-order h-, and higher-order p-version finite elements developed for axisymmetrically loaded cylindrical shells is investigated by two representative model problems. It is numerically proven that no negative effect can be experienced when the thickness is small and tends to zero.     

Confocal Fluorescence Detected Linear Dichroism Imaging of Isolated Human Amyloid Fibrils. Role of Supercoiling

Amyloids are highly organized insoluble protein aggregates that are associated with a large variety of degenerative diseases. In this work, we investigated the anisotropic architecture of isolated human amyloid samples stained with Congo Red. This was performed by fluorescence detected linear dichroism (FDLD) imaging in a laser scanning confocal microscope that was equipped with a differential polarization attachment using high frequency modulation of the polarization state of the laser beam and a demodulation circuit. Two- and three-dimensional FDLD images of amyloids provided information on the orientation of the electric transition dipoles of the intercalated Congo Red molecules with unprecedented precision and spatial resolution. We show that, in accordance with linear dichroism imaging (Jin et al. Proc Natl Acad Sci USA 100:15294, 2003), amyloids exhibit strong anisotropy with preferential orientation of the dye molecules along the fibrils; estimations on the orientation angle, of around 45°, are given using a model calculation which takes into account the helical organization of the filaments and fibrils. Our data also show that FDLD images display large inhomogeneities, high local values with alternating signs and, in some regions, well identifiable μm-sized periodicities. These features of the anisotropic architecture are accounted for by supercoiling of helically organized amyloid fibrils.     

A desk computer program for the calculation of rate constants

A desk computer program has been written in BASIC programming language to optimize the values of rate constants determined from kinetic measurements of time and concentration data. The program is capable of the simultaneous refinement of a maximum of 5 rate constants. A FORTRAN version using the Gear method is also available.

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