Q2 dependence of the neutron spin structure function g2(n) at low Q2

We present the first measurement of the Q2 dependence of the neutron spin structure function g2(n) at five kinematic points covering 0.57 (GeV/c)2 < or = Q2 < or = 1.34 (GeV/c)2 at x approximately = 0.2. Though the naive quark-parton model predicts g2 = 0, nonzero values occur in more realistic models of the nucleon which include quark-gluon correlations, finite quark masses, or orbital angular momentum. When scattering from a noninteracting quark, g2(n) can be predicted using next-to-leading order fits to world data for g1(n). Deviations from this prediction provide an opportunity to examine QCD dynamics in nucleon structure. Our results show a positive deviation from this prediction at lower Q2, indicating that contributions such as quark-gluon interactions may be important. Precision data obtained for g1(n) are consistent with next-to-leading order fits to world data.     

Wave chaos in real-world vertical-cavity surface-emitting lasers

We report the onset of wave chaos in a real-world vertical-cavity surface-emitting laser. In a joint experimental and modeling approach we demonstrate that a small deformation in one layer of the complicated laser structure changes the emission properties qualitatively. Based on the analysis of the spatial emission profiles and spectral eigenvalue spacing distributions, we attribute these changes to the transition from regular behavior to wave chaos, and justify the full analogy to two-dimensional billiards by model calculations. Hence, these lasers represent fascinating devices for wave chaos studies.     

Mesomorphic properties of cyanobiphenyl dimers with a central malonate unit

A series of cyanobiphenyl dimers attached via alkoxy spacers to a central malonate were prepared, and the mesomorphic behaviour was studied by differential scanning calorimetry (DSC), polarised optical microscopy and X-ray diffraction (Wide-angle X-ray scattering and Small-angle X-ray scattering). Depending on spacer lengths and substitution of the malonate, nematic and smectic A mesophases with pronounced odd–even effect were observed. C-2-unsubstituted malonates formed nematic phases for chain lengths C₆–C₁₄, while C₁₂ and C₁₄ homologues displayed additional smectic A phases. In contrast, malonates with fluorinated tails at C-2 displayed exclusively smectic A phases. Remarkably, the X-ray diffraction profile of the smectic A phase of the C-2-unsubstituted C₁₂ malonate showed a fundamental (001) and the corresponding third-order (003) diffraction peak, but no (002) reflection. Using Fourier analysis, the diffraction pattern was converted to an electron density profile, which was in good agreement with the proposed packing model of the SmA mesophase based on a horseshow- or hairpin-like conformation of the malonate.     

Chitosan-encapsulated Keggin Anion [Ti2W10PO40]7−. Synthesis, Characterization and Cellular Uptake Studies

The Keggin type polyoxotungstate [Ti₂W₁₀PO₄₀]⁷⁻ forms stable associates with the biopolymer chitosan in the nanometer size range. The cluster compound crystallizes from aqueous solution as K₄H₃[Ti₂W₁₀PO₄₀] · 15H₂O having a tetragonal structure. Both, the cluster compound and the chitosan/[Ti₂W₁₀PO₄₀] associates show a high hydrolytic stability at pH 7.4. The associates formed between the cluster anion [Ti₂W₁₀PO₄₀]⁷⁻ with the polyaminosaccharide chitosan have been characterized by photon correlation spectroscopy, scanning electron microscopy, filtration, centrifugation and zeta potential measurements. The size of the associates formed is in the range of ca. 5×10¹ to 5×10² nm. These particles have a defined stoichiometry with 5–6 cluster anions bound per molecule chitosan. The isoelectric point determined by zeta potential measurements was found for a cluster anion to chitosan molar ratio of 5.5, indicating the charge neutralization between protonated chitosan and [Ti₂W₁₀PO₄₀]⁷⁻ anions. Cellular uptake studies with [Ti₂W₁₀PO₄₀]⁷⁻ using tumor cell lines FaDu (human squamous carcinoma) and HT-29 (human adenocarcinoma) showed that the tungsten amount inside the cells is remarkably enhanced in the presence of chitosan.     

Unified molecular picture of the surfaces of aqueous acid, base, and salt solutions

The molecular structure of the interfacial regions of aqueous electrolytes is poorly understood, despite its crucial importance in many biological, technological, and atmospheric processes. A long-term controversy pertains between the standard picture of an ion-free surface layer and the strongly ion specific behavior indicating in many cases significant propensities of simple inorganic ions for the interface. Here, we present a unified and consistent view of the structure of the air/solution interface of aqueous electrolytes containing monovalent inorganic ions. Molecular dynamics calculations show that in salt solutions and bases the positively charged ions, such as alkali cations, are repelled from the interface, whereas the anions, such as halides or hydroxide, exhibit a varying surface propensity, correlated primarily with the ion polarizability and size. The behavior of acids is different due to a significant propensity of hydronium cations for the air/solution interface. Therefore, both cations and anions exhibit enhanced concentrations at the surface and, consequently, these acids (unlike bases and salts) reduce the surface tension of water. The results of the simulations are supported by surface selective nonlinear vibrational spectroscopy, which reveals among other things that the hydronium cations are present at the air/solution interface. The ion specific propensities for the air/solution interface have important implications for a whole range of heterogeneous physical and chemical processes, including atmospheric chemistry of aerosols, corrosion processes, and bubble coalescence.     

A convenient room temperature polycondensation toward hyperbranched AB2‐type all‐aromatic polyesters with phenol terminal groups

As a convenient alternative to the classical melt polycondensation the one‐pot solution polycondensation of suitable AB₂ monomers under mild conditions has been successfully adapted to hyperbranched all‐aromatic polyester with phenol terminal groups. The polymerization was performed in solution at room temperature directly using commercially available 3,5‐dihydroxybenzoic acid as monomer and 4‐(dimethylamino) pyridinium 4‐tosylate as catalyst to suppress the formation of N‐acylurea. Different carbodiimides as coupling agents were investigated to find the optimal esterification conditions. The polymers have been characterized extensively and were compared with their well‐known analogs synthesized in melt. The characterization was carried out by NMR spectroscopy, size exclusion chromatography, and asymmetric flow‐field flow fractionation as an alternative separation technique for multifunctional polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5158–5168, 2009     

Modeling and simulation of extrusion of aluminum alloys

The purpose of this work is the modeling and simulation of the material behavior of aluminum alloys during extrusion, cooling and metal forming processes. In particular, the alloys of the 6000 series (Al-Mg-Si) and 7000 series (Al-Zn-Mg) are relevant here. Under the corresponding conditions, their behavior is controlled mainly by dynamic recovery during the extrusion and static recrystallization during cooling. The current material model is based on the role of the energy stored in the material during extrusion as the driving force for microstructural evolution. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)