Compatibility conditions for a left Cauchy-Green strain field

This paper deals chiefly with various issues pertaining to the existence and uniqueness of a finite deformation that gives rise to a prescribed right or left Cauchy-Green strain-tensor field.Following a review and discussion of available existence and uniqueness theorems appropriate to a pre-assigned right strain field, the extent of uniqueness of a generating deformation is established under minimal smoothness and invertibility assumptions.The remainder of the paper is devoted to the more involved corresponding existence and uniqueness questions for a given left strain-tensor field. These questions are first discussed in a three-dimensional setting and are then resolved for the special class of plane deformations. The results thus obtained stand in marked contrast to their counterparts for a given right strain field.     

Spectroscopy of195Hg and196Hg

High-spin states in the oblate-deformed nuclei¹⁹⁵Hg and¹⁹⁶Hg were populated in the¹⁹⁸Pt(α, xn) reaction and investigated by in-beamγ-ray spectroscopy using six Compton-suppressed Ge detectors. The level schemes of both nuclei are extended considerably. The level structure is interpreted within the framework of the cranked shell model. Good agreement is obtained between model predictions and experimental results.     

Untersuchung von Braunoxidkatalysatoren mit Hilfe des MÖSSBAUER-Effektes

The pre-use state of industrial α-Fe₂O₃/Cr₂O₃ CO-conversion catalysts of known activity has been investigated by means of MÖSSBAUER effect and BET measurements. The iron of various catalyst samples has been found at room and catalytic reaction temperature (330°C) to be as well in the antiferro- as in the paramagnetic state, the ratio of both states being strongly dependent on temperature and on the specific catalyst sample. As the main reason for the occurrence of these two states within each sample the simultaneous occurrence of differently sized powder particles may be supposed. The ratio difference between one and another sample is due to differing chemical composition and grain size. Since no correlation was found between these resulats, BET surface data, grain size distribution and/or catalytic activity, pore structure differences are assumend to explain the observed differences in sample activity.     

Helical nanofibers of self-assembled bipolar phospholipids as template for gold nanoparticles

Bipolar phospholipids (bolalipids) represent an exciting class of amphiphilic molecules as they self-assemble in water to distinct structures of nanoscopic dimensions. Reported here are structural details of helical nanofibers, composed of achiral, symmetrical single-chain bolalipids with phosphocholine headgroups. These nanofibers are used as template for the fixation of gold nanoparticles (AuNPs) without prior functionalization. This realization of a metal array on bolalipid nanofibers is one of the rare examples of one-dimensional AuNP arrangements in solution. The loading and the heat of binding of AuNPs are determined applying transmission electron microscopy and isothermal titration calorimetry.     

Structural and Chemical Properties of NiOx Thin Films: Oxygen Vacancy Formation in O2 Atmosphere

NiO_x films on Si(111) were put in contact with oxygen at elevated temperatures. During heating and cooling in oxygen atmosphere Near Ambient Pressure (NAP)-XPS and -XAS and work function (WF) measurements reveal the creation and replenishing of oxygen vacancies in dependence of temperature. Oxygen vacancies manifest themselves as a distinct O1s feature at 528.9 eV on the low binding energy side of the main NiO peak as well as by a distinct deviation of the Ni2p_3/2 spectral features from the typical NiO spectra. DFT calculations reveal that the presence of oxygen vacancies leads to a charge redistribution and altered bond lengths of the atoms surrounding the vacancies causing the observed spectral changes. Furthermore, we observed that a broadening of the lowest energy peak in the O K-edge spectra can be attributed to oxygen vacancies. In the presence of oxygen vacancies, the WF is lowered by 0.1 eV.     

Structure-property relationship in stimulus-responsive bolaamphiphile hydrogels

The formation of temperature-, concentration-, and pH-responsive hydrogels composed of the symmetric long-chain bolaamphiphile dotriacontane-1,1'-diyl bis[[2-(dimethylammonio)ethyl]phosphate] (Me(2)PE-C32-Me(2)PE) was investigated by rheological, scattering, and spectroscopic techniques. At pH 5, this bolaamphiphile is known to form a dense network of helically structured nanofibers (K?hler et al. Soft Matter 2006, 2, 77-86). Rheological measurements and dynamic light scattering were used to describe the macroscopic behavior of the hydrogels. Small-angle neutron scattering (SANS) and time-resolved static light scattering were applied to get information about the morphology of the self-assembled aggregates. Finally, solid-state 31P NMR spectroscopy was used to gain insight into the mobility of the bolaamphiphile molecules within the fiber aggregates. In comparison with the previously examined trimethylammonio analogue PC-C32-PC, which forms temperature-dependent hydrogels, Me(2)PE-C32-Me(2)PE exhibits additional concentration- and pH-dependent gelling properties. The significantly higher stability of the Me(2)PE-C32-Me(2)PE hydrogel is supported by the SANS data, which indicate the presence of fiber aggregates up to 50 degrees C.     

General synthesis and aggregation behaviour of a series of single-chain 1,omega-bis(phosphocholines)

The synthesis and physicochemical characterisation of a series of polymethylene-1,omega-bis(phosphocholines) with even-numbered chain lengths between 22 and 32 carbon atoms is described. Two new synthetic strategies for the preparation of long-chain 1,omega-diols as hydrocarbon building blocks are presented. The temperature-dependent self-assembly of the single-chain bolaamphiphiles was investigated by cryo transmission electron microscopy (cryo-TEM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR).     

Membranolytic activity of bile salts: influence of biological membrane properties and composition

The two main steps of the membranolytic activity of detergents: 1) the partitioning of detergent molecules in the membrane and 2) the solubilisation of the membrane are systematically investigated. The interactions of two bile salt molecules, sodium cholate (NaC) and sodium deoxycholate (NaDC) with biological phospholipid model membranes are considered. The membranolytic activity is analysed as a function of the hydrophobicity of the bile salt, ionic strength, temperature, membrane phase properties, membrane surface charge and composition of the acyl chains of the lipids. The results are derived from calorimetric measurements (ITC, isothermal titration calorimetry). A thermodynamic model is described, taking into consideration electrostatic interactions, which is used for the calculation of the partition coefficient as well as to derive the complete thermodynamic parameters describing the interaction of detergents with biological membranes (change in enthalpy, change in free energy, change in entropy etc). The solubilisation properties are described in a so-called vesicle-to-micelle phase transition diagram. The obtained results are supplemented and confirmed by data obtained from other biophysical techniques (DSC differential scanning calorimetry, DLS dynamic light scattering, SANS small angle neutron scattering).