Differential cross sections of proton compton scattering at photon laboratory energies between 1.2 and 1.7 GeV

Zeitschrift für Physik C Particles and Fields - Differential cross sections of proton Compton scattering have been measured at the Bonn 2.5 GeV synchrotron. The experiment covers photon...     

Quantitative vibrational dynamics of iron in nitrosyl porphyrins

We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of the Fe atom in porphyrins designed to model heme protein active sites. Nuclear resonance vibrational spectroscopy (NRVS) yields frequencies, amplitudes, and directions for 57Fe vibrations in a series of ferrous nitrosyl porphyrins, which provide a benchmark for evaluation of quantum chemical vibrational calculations. Detailed normal mode predictions result from DFT calculations on ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), its cation [Fe(TPP)(NO)]+, and ferrous nitrosyl porphine Fe(P)(NO). Differing functionals lead to significant variability in the predicted Fe-NO bond length and frequency for Fe(TPP)(NO). Otherwise, quantitative comparison of calculated and measured Fe dynamics on an absolute scale reveals good overall agreement, suggesting that DFT calculations provide a reliable guide to the character of observed Fe vibrational modes. These include a series of modes involving Fe motion in the plane of the porphyrin, which are rarely identified using infrared and Raman spectroscopies. The NO binding geometry breaks the four-fold symmetry of the Fe environment, and the resulting frequency splittings of the in-plane modes predicted for Fe(TPP)(NO) agree with observations. In contrast to expectations of a simple three-body model, mode energy remains localized on the FeNO fragment for only two modes, an N-O stretch and a mode with mixed Fe-NO stretch and FeNO bend character. Bending of the FeNO unit also contributes to several of the in-plane modes, but no primary FeNO bending mode is identified for Fe(TPP)(NO). Vibrations associated with hindered rotation of the NO and heme doming are predicted at low frequencies, where Fe motion perpendicular to the heme is identified experimentally at 73 and 128 cm-1. Identification of the latter two modes is a crucial first step toward quantifying the reactive energetics of Fe porphyrins and heme proteins.     

Novel electrodeposition behavior of Ni on porous anodic alumina templates without a conductive interlayer

During template-assisted electrodeposition, single-crystalline metallic nanowires could be obtained only when the overpotential is low. However, an unusual electrodeposition behavior on the PAA/Si substrate without a conductive interlayer between the template and Si is described in the present study. Through the electrical breakdown of the template, Ni nanodots, nanowires and nanotubes could be obtained by only changing the electrodeposition voltage on the same substrate. The mechanisms leading to the formation of various nanostructures are described in detail and compared with those for the conventional template-assisted electrodeposition process. The electrodeposition first occurred on the pore wall instead of from the underlying substrate, leading to the formation of some Ni nanotubes at a more negative voltage. Besides, single-crystalline Ni nanowires could also be formed even when the electrodeposition voltage was as negative as -40 V, indicating that the formation of single-crystalline metallic nanowires under a large overpotential is possible.     

Hypochlorous acid-induced membrane pore formation in red blood cells

The hyperproduction of hypochlorous acid (HOCl), an extremely toxic biological oxidant generated by neutrophils and monocytes, is involved in the pathogenesis of many diseases. In these studies, we attempted to determine the membrane and cellular events associated with HOCl-induced erythrocyte impairment and haemolysis. In vitro human erythrocyte exposure to HOCl (0.1-1.0 mM) resulted in rapid oxidation of reduced glutathione, an increase in cell osmotic fragility and the formation of transient membrane pores. The process of glutathione oxidation depended on the [oxidant]/[cell number] ratio. The HOCl-induced haemolysis observed was apparently mediated by pore formation and altered membrane electrolyte permeability. The estimated pore radius was approximately 0.7 nm and the average number per cell was 0.01. The rate constant of HOCl-produced haemolysis depended on pH. There were significant differences in haemolysis of HOCl-treated erythrocytes which had maximal stability at pH 7.2-7.3.     

A remark on the ring of algebraic integers in $$\mathbb{Q}(\sqrt { - d} )$$

It is well-known that the rings O_d of algebraic integers in \(\mathbb{Q}(\sqrt { - d} )\) for d = 19, 43, 67, and 163 are principal ideal domains but not Euclidean. In this article we shall provide a method, based on a result of P. M. Cohn, to construct explicitly pairs (b, a) of integers in O_d for d = 19, 43, 67, and 163 such that, in O_d, there exists no terminating division chain of finite length starting from the pairs (b, a). That is, a greatest common divisor of the pairs (b, a) exists in O_d but it can not be obtained by applying a terminating division chain of finite length starting from (b, a). Furthermore, for squarefree positive integer d ? {1, 2, 3, 7, 11, 19, 43, 67, 163}, we shall also construct pairs (b, a) of integers in O_d which generate O_d but have no terminating division chain of finite length. It is of interest to note that our construction provides a short alternative proof of a theorem of Cohn which is related to the concept of GE₂-rings.     

Fabrication of aligned TiO2 one-dimensional nanostructured arrays using a one-step templating solution approach

In this letter, we report a one-step templating synthetic strategy to prepare aligned TiO2 nanotube and nanowire arrays on Si substrate from a solution at ambient temperature. The deposition of TiO2 and the selective-etching of the ZnO template proceeded at the same time through the careful control of process parameters. The different thickness of TiO2 sheaths, leading to the formation of nanotubes or nanorods, can be precisely controlled by the deposition time. The idea of selective etching and deposition is applicable to other oxide materials, and such a facile method is expected to find widespread applications.     

Photoacoustic calorimetry and quantum yields of Mo(CO)(6) ligand exchange in linear alkanes: determination of volume of reaction, energetics, and kinetics of nucleophile displacement of alkane from Mo(CO)(5)(alkane).

Photoacoustic calorimetry (PAC) and actinometry studies were used to determine the enthalpies and volumes of reaction for the production of a transient intermediate, Mo(CO)(5)-alkane, and for its subsequent reaction with tetrahydrofuran (THF). Both the enthalpy and the volume of reaction contribute to the photoacoustic signal and have been resolved by changing the solvent thermal expansion properties with a series of linear alkanes. The enthalpies for substitution of CO on Mo(CO)(6) by an alkane and of coordinated alkane on Mo(CO)(5)(alkane) by THF are 30 and -14 kcal/mol, respectively. Likewise, the volumes of reaction are 18 and -1 mL/mol. From available data for the Mo--CO bond energy, these results allow the calculation of the Mo-alkane and Mo-THF bond energies (11 and 25 kcal/mol, respectively). The Mo-alkane result is 7 kcal/mol less than that from our previous PAC study, which ignored the volume of reaction, and is in better agreement with the results of kinetic studies. The large absolute difference in the reaction volumes for each step is partially attributed to a void volume created during the formation of the Mo--THF bond. In general, the volume of reaction cannot be neglected in the calculation of enthalpies of ligand substitution from PAC studies. The quantum yields for photosubstitution of Mo(CO)(6), in contrast to Cr(CO)(6), were found to be insensitive to the chain length of the alkane solvent.     

Effective results on compositions of nonexpansive mappings

This paper provides uniform bounds on the asymptotic regularity for iterations associated to a finite family of nonexpansive mappings. We obtain our quantitative results in the setting of (r,δ)$(r,\delta )$-convex spaces, a class of geodesic spaces which generalizes metric spaces with a convex geodesic bicombing.     

An application of proof mining to nonlinear iterations

In this paper we apply methods of proof mining to obtain a highly uniform effective rate of asymptotic regularity for the Ishikawa iteration associated with nonexpansive self-mappings of convex subsets of a class of uniformly convex geodesic spaces. Moreover, we show that these results are guaranteed by a combination of logical metatheorems for classical and semi-intuitionistic systems.