Miniaturized Compression Test at Very High Strain Rates by Direct Impact

A modified miniaturized version of the Direct Impact Compression Test (DICT) technique is described in this paper. The method permits determination of the rate-sensitive plastic properties of materials up to strain rate ∼10⁵ s⁻¹. Miniaturization of the experimental setup with specimen dimensions: diameter d _S = 2.0 mm and thickness l _S = 1.0 mm, Hopkinson bar diameter 5.2 mm, with application of a novel optical arrangement in measurement of specimen strain, makes possible compression tests at strain rates from ∼10³ s⁻¹ to ∼10⁵ s⁻¹. In order to estimate the rate sensitivity of a low-alloy construction steel, quasi-static, Split Hopkinson Pressure Bar (SHPB) and DICT tests have been performed at room temperature within the rate spectrum ranging from 5*10⁻⁴ s⁻¹ to 5*10⁴ s⁻¹. Adiabatic heating and friction effects are analyzed and the final true stress versus true strain curves at different strain rates are corrected to a constant temperature and zero friction. The results have been analyzed in the form of true stress versus the logarithm of strain rate and they show two regions of a constant rate sensitivity : relatively low up to the strain rate threshold ∼50 s⁻¹, and relatively high above the threshold, up to strain rate ∼4.5*10⁴ s⁻¹.     

Evaluation of Spin Relaxation Induced by Chemical Shielding Anisotropy: A Comment on the Importance of the Antisymmetric Component

General comments related to the impact of the antisymmetric component of the electronic shielding tensor in context of nuclear magnetic relaxation studies are given. It is argued that in most conceivable applications of high field NMR, the effects associated with the antisymmetric component will be negligible. However, in certain situations, this conventional wisdom may fail and, as an extreme example, it is demonstrated that for highly nonaxially symmetric shieldings, motional anisotropy may accentuate dramatically therelativeimportance of the antisymmetry.     

Inclusion complexes of cryptophane-E with dichloromethane and chloroform: A thermodynamic and kinetic study using the 1D-EXSY NMR method

Complexation equilibria and kinetics of exchange of chloroform and dichloromethane molecules between the cavity of cryptophane-E and bulk solution were investigated using NMR methods. Using one-dimensional magnetization transfer (1D-EXSY type sequence), chemical exchange rates were measured in different temperature ranges, limited by the equilibrium constant values of the complexes and the boiling points of the guest substances. From the kinetic data, activation energies were calculated using the Arrhenius equation. From the temperature-dependence of the association constant data, the enthalpy and entropy of complexation were estimated and compared with values for similar complexes of other cryptophanes.     

Magnetic Fe doped ZnO nanofibers obtained by electrospinning

We demonstrate structural and room temperature magnetic properties of Fe doped ZnO nanofibers (NFs) obtained by electrospinning followed by calcination. The observed NFs, formed from crystalographically oriented, approximately 4.5?nm particles conglomerates, were approximately 200?nm in diameter. The reported synthesis of room temperature ferromagnetic Fe doped ZnO NFs is both facile and economical, and is therefore suggested as a generic method of fabricating biocompatible magnetic materials. The major substrates selected for the NFs synthesis (Zn, Fe) comprised of relatively low toxicity materials. Incorporating 10% Fe into ZnO does not modify the wurtzite crystal structure of the host material. No evidence of impurity phase was detected by either X-ray or electron diffraction. Magnetometry studies and Magnetic Force Microscopy imaging reveal a local ferromagnetic order that persists up to room temperature. We suggest that the observed phenomenon is either due to a mechanism mediated by presence of oxygen vacancies and/or is related to iron-rich precipitates.     

Deuteron magnetic resonance of monodeuteroethene: Isotropic and anisotropic phase spectra

Deuteron magnetic resonance spectrum of monodeuteroethene in isotropic phase solution is shown to give the relative signs of the indirect spin-spin coupling constants, while the proton spectrum cannot provide this information. In agreement with previous experimental and theoretical evidence, J _gem is found to have the same sign as the two vicinal coupling constants. High resolution deuteron resonance spectra of monodeuteroethene in the nematic phase solution are analysed in terms of the order matrix and quadrupole splitting. The quadrupole coupling constant and the asymmetry parameter are determined by two partly independent methods.     

On the Generation of Timed Discrete Approximations for Continuous Systems

In this contribution we present two procedures to systematically derive timed discrete approximations from continuous models. Both methods are based on a rectangular state space partition and aim at mapping continuous dynamic behaviours described by ODE-systems with switched inputs onto timed state transition systems: In the first approach the transitions between the discrete states are determined by analysing the flow between rectangular cells of the state space. The second one uses numerical integration of the ODE-system between partitions of the boundaries of the cells. The application of both approaches is illustrated by a chemical process example. The paper discusses completeness and consistency properties of the approximation mappings as well as issues of accuracy and computational effort.     

High-throughput analysis of therapeutic and diagnostic monoclonal antibodies by multicapillary SDS gel electrophoresis in conjunction with covalent fluorescent labeling

Capillary gel electrophoresis (CGE) in the presence of sodium dodecyl sulfate (SDS) is a well-established and widely used protein analysis technique in the biotechnology industry, and increasingly becoming the method of choice that meets the requirements of the standards of International Conference of Harmonization (ICH). Automated single channel capillary electrophoresis systems are usually equipped with UV absorbance and/or laser-induced fluorescent (LIF) detection options offering general applicability and high detection sensitivity, respectively; however, with limited throughput. This shortcoming is addressed by the use of multicapillary gel electrophoresis (mCGE) systems with LED-induced fluorescent detection (LED-IF), also featuring automation and excellent detection sensitivity, thus widely applicable to rapid and large-scale analysis of biotherapeutics, especially monoclonal antibodies (mAb). The methodology we report in this paper is readily applicable for rapid purity assessment and subunit characterization of IgG molecules including detection of non-glycosylated heavy chains (NGHC) and separation of possible subunit variations such as truncated light chains (Pre-LC) or alternative splice variants. Covalent fluorophore derivatization and the mCGE analysis of the labeled IgG samples with multi-capillary gel electrophoresis are thoroughly described. Reducing and non-reducing conditions were both applied with and without peptide N-glycosidase F mediated deglycosylation.     

Extensive NMRD studies of Ni(II) salt solutions in water and water-glycerol mixtures

Aqueous solutions of simple nickel(II) salts are a classical test case for theories of the paramagnetic relaxation enhancement (PRE) and its dependence on the magnetic field (nuclear magnetic relaxation dispersion, NMRD), going back to late fifties. We present here new experimental data, extending the NMRD range up to 21T (900 MHz). In addition to salt solutions in (acidified) water, we have also measured on solutions containing glycerol. The aqueous solution data do not show any significant changes compared to the earlier experiments. The interpretation, based on the general ("slow-motion") theory is also similar to the earlier work from our laboratory. The NMRD-data in mixed solvents are qualitatively different, indicating that the glycerol not only changes the solution viscosity, but may also enter the first coordination sphere of the metal ion, resulting in lower symmetry complexes, characterized by non-vanishing averaged zero-field splitting. This hypothesis is corroborated by molecular dynamics simulations. A strategy appropriate for interpreting the NMRD-data for the chemically complicated systems of this type is proposed.     

Nuclear spin relaxation in paramagnetic systems (S>/=1) under fast rotation conditions

A new theoretical model for nuclear spin relaxation in paramagnetic systems in solution has been developed. Fast rotational motion is included in the model, both as a source of modulation of the static zero-field splitting, which provides a mechanism for electron spin relaxation, and as an origin of the stochastic variation of the electron spin-nuclear spin dipole-dipole interaction leading to nuclear spin relaxation. At the limit of low magnetic field, the model is essentially identical to the earlier formulations from our laboratory, but new closed-form expressions are given for the inner- and outer-sphere relaxation at the high-field limit. Numerical comparisons with a general theory are reported for the inner-sphere case. In addition, some nuclear magnetic relaxation dispersion (NMRD) profiles from the literature are considered for systems where experiments have been done with both low-molecular weight paramagnetic complexes and their adducts with proteins. Previously developed theories are used to interpret data for the slowly rotating protein adducts, and good fits of the fast-rotating counterparts are obtained by further adjustment of one or two additional parameters.     

Propagation of ultrasonic waves and anomalies nearT c in single crystalline YBa2Cu3O7−x high-T c superconductors

The attenuation and the velocity of ultrasonic waves in single crystalline high-T _c YBa₂Cu₃O_7–x have been measured in the temperature range from 3 to 280 K for the C₁₁-, C₃₃-, C₄₄- and C₆₆-mode. At the superconducting transition a pronounced peak in the absorption is observed for the longitudinal C₁₁-mode. The longitudinal C₁₁- and C₃₃-modes and the transverse C₄₄-mode exhibit a plateau in the temperature dependence of the velocity. The temperature dependence of the absorption of the transverse C₄₄-mode reveals a change in the slope atT _c. The data are compared with the predictions derived from a thermodynamic treatment and with the results of measurements on coarse grain and fine grain sintered and sinter-forged materials.