Nonlinear magneto-optical Bragg gratings

In magneto-optical gratings the magnetic dipolar coupling superimposed on the electric dipolar one introduces nonreciprocity and spectral discrimination between circular polarization states, measured by a Zeeman-like splitting of the photonic Bragg resonances. In a nonlinear regime the degree of nonreciprocity is modified by the photoinduced interplay of these splittings and their Stark-like shifts. We predict novel magneto-optical modulation schemes for switching between orthogonal circular polarization states of transmission or reflection operated by means of an intense linearly polarized optical pulse train.     

Relating chromatographic retention and electrophoretic mobility to the ion distribution within electrosprayed droplets

Ions that are observed in a mass spectrum obtained with electrospray mass spectrometry can be assumed to originate preferentially from ions that have a high distribution to the surface of the charged droplets. In this study, a relation between chromatographic retention and electrophoretic mobility to the ion distribution (derived from measured signal intensities in mass spectra and electrospray current) within electrosprayed droplets for a series of tetraalkylammonium ions, ranging from tetramethyl to tetrapentyl, is presented. Chromatographic retention in a reversed-phase system was taken as a measure of the analyte’s surface activity, which was found to have a large influence on the ion distribution within electrosprayed droplets. In addition, different transport mechanisms such as electrophoretic migration and diffusion can influence the surface partitioning coefficient. The viscosity of the solvent system is affected by the methanol content and will influence both diffusion and ion mobility. However, as diffusion and ion mobility are proportional to each other, we have, in this study, chosen to focus on the ion mobility parameter. It was found that the influence of ion mobility relative to surface activity on the droplet surface partitioning of analyte ions decreases with increasing methanol content. This effect is most probably coupled to the decrease in droplet size caused by the decreased surface tension at increasing methanol content. The same observation was made upon increasing the ionic strength of the solvent system, which is also known to give rise to a decreased initial droplet size. The observed effect of ionic strength on the droplet surface partitioning of analyte ions could also be explained by the fact that at higher ionic strength, a larger number of ions are initially closer to the droplet surface and, thus, the contribution of ionic transport from the bulk liquid to the liquid/air surface interface (jet and droplet surface), attributable to migration or diffusion will decrease.     

Metal ion interaction with phosphorylated tyrosine analogue monolayers on gold

Phosphorylated tyrosine analogue molecules (pTyr-PT) were assembled onto gold substrates, and the resulting monolayers were used for metal ion interaction studies. The monolayers were characterized by X-ray photoelectron spectroscopy (XPS), infrared reflection-absorption spectroscopy (IRAS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), both prior to and after exposure to metal ions. XPS verified the elemental composition of the molecular adsorbate and the presence of metal ions coordinated to the phosphate groups. Both the angle-dependent XPS and IRAS results were consistent with the change in the structural orientation of the pTyr-PT monolayer upon exposure to metal ions. The differential capacitance of the monolayers upon coordination of the metal ions was evaluated using EIS. These metal ions were found to significantly change the capacitance of the pTyr-PT monolayers in contrast to the nonphosphorylated tyrosine analogue (TPT). CV results showed reduced electrochemical blocking capabilities of the phosphorylated analogue monolayer when exposed to metal ions, supporting the change in the structure of the monolayer observed by XPS and IRAS. The largest change in the structure and interfacial capacitance was observed for aluminum ions, compared to calcium, magnesium, and chromium ions. This type of monolayer shows an excellent capability to coordinate metal ions and has a high potential for use as sensing layers in biochip applications to monitor the presence of metal ions.     

Iron-catalyzed cross-coupling of imidoyl chlorides with Grignard reagents

[reaction: see text] A general, high yielding rapid iron-catalyzed cross-coupling reaction between Grignard reagents and imidoyl chlorides is described. These reactions are typically completed within 5 min, resulting in high yields of 71-96% using 5% iron catalyst in a THF-NMP solvent mixture. Functionalized imidoyl chlorides (e.g., R = CO(2)Me) gave excellent yields (89%).     

Photon echo spectroscopy of porphyrins and heme proteins: effects of quasidegenerate electronic structure on the peak shift decay

Three pulse photon echo peak shift spectroscopy and transient grating measurements on Zn-substituted cytochrome c, Zn-tetraphenylporphyrin, and Zn-protoporphyrin IX are reported. The effects of protein conformation, axial ligation, and solvent are investigated. Numerical simulations of the peak shift and transient grating experiments are presented. The simulations employed recently derived optical response functions for square-symmetric molecules with doubly degenerate excited states. Simulations exploring the effects of excited-state energy splitting, symmetric and asymmetric fluctuations, and excited-state lifetime show that the time scales of the peak shift decay in the three-level system largely reflect the same dynamics as in the two-level system. However, the asymptotic peak shift, which is a clear indicator of inhomogeneous broadening in a two-level system, must be interpreted more carefully for three-level systems, as it is also influenced by the magnitude of the excited-state splitting. The calculated signals qualitatively reproduce the data.     

Defect-induced strong ferromagnetism in Cr-doped In2O3 from first-principles theory

We demonstrate by means of first-principles calculations that the high Curie temperature observed in Cr-doped In₂O₃ is mediated by intrinsic p-type defects, namely In vacancies or O interstitials. Charge transfer from Cr 3d states to the hole states formed by these defects makes Cr ions in the mixed valence state, giving rise to a strong ferromagnetic coupling. Calculated formation energies of various defects also show that doping Cr in In₂O₃ could greatly lower the formation energies of p-type intrinsic defects even in oxygen-deficient growth conditions. These results advance our understanding of the underlying physics of diluted magnetic oxides.     

On the Representation of Functions with Gaussian Wave Packets

We introduce Gaussian wave packets in pursuit of representations of functions, in which the representation is invariant under translation, modulation, scale, rotation and anisotropic dilation. Properties of both continuous and discrete representations are discussed. For the discrete (two-dimensional) case, we develop fast algorithms for the application of the analysis and synthesis operators. A main objective for using Gaussian wave packets is to obtain sparse approximations of functions. However, due to the many invariance properties, the representations will have a high degree of redundancy. Therefore, we also introduce sparse methods for highly redundant representations, that employ some of the analytic properties of Gaussian wave packet for gaining computational efficiency.     

Parallel algorithm of 3D wave-packet decomposition of seismic data: Implementation and optimization for GPU

In this paper, we consider 3D wave-packet transform that is useful in 3D data processing. This transform is computationally intensive even though it has a computational complexity of O(N³ log N). Here we present its implementation on GPUs using NVIDIA CUDA technology. The code was tested on different types of graphical processors achieving the average speedup up to 46 times on Tesla M2050 compared to CPU sequential code. Also, we analyzed its scalability for several GPUs. The code was tested for processing synthetic seismic data set: data compression, de-noising, and interpolation.     

A practical synthesis of [C4] N-benzylpiperazine from [C2] glycine

A high yielding gram-scale synthesis of [¹³C₄] N-benzylpiperazine for use as a convenient and versatile building block in isotope labeling studies of clinical drug candidates is reported.