The multiple hydrogen location near a α-Fe vacancy

The interaction between 10 hydrogen atoms and a α-Fe structure having a vacancy (V) has been studied using a cluster model and a semi-empirical theoretical method. The energy of the system was calculated by the atom superposition and electron delocalization molecular orbital method. The electronic structure was studied using the concept of density of states and crystal orbital overlap population curves.For the study of a sequential absorption, the hydrogen atoms were positioned in their energy minima configurations, near to the tetrahedral sites neighboring the vacancy, except the last H atom that was located far from the vacancy. The energy difference for H agglomeration was also computed. The vacancy-H_n complexes become less stable than VH species for more than three hydrogen's.The changes in the electronic structure of Fe atoms near the vacancy were also analyzed. The interactions mainly involve Fe 3d and 4s atomic orbitals. The contribution of Fe p orbitals is much less important. The Fe-Fe bond weakened as new Fe-H and H-H pairs were formed. The effect of H atoms is limited to its first Fe neighbors. The detrimental effect of H atoms on the Fe-Fe bonds can be related to the mechanism for embrittlement in α-Fe.     

An efficient method for the N-arylation of phenylurea via copper catalyzed amidation

The coupling reaction of phenylurea with different functionalized aryl halides in the presence of air stable CuI,N,N-dimethylethylenediamine as a ligand,and K₃PO₄ as a base gives symmetrical and unsymmetrical diarylureas in relatively high yields.This method is milder than the palladium catalyzed arylation and avoids the use of toxic phosphine ligands.     

A guided wave technique for the characterization of highly attenuative viscoelastic materials

The measurement of the acoustic properties of highly attenuative materials such as bitumen is very difficult. One possibility is to use measurements of the extent to which filling a cylindrical waveguide with the material affects the dispersion relationship of the cylinder. Torsional modes have been excited using piezoelectric transducers placed at one end of the cylinder, while the phase velocity and attenuation spectra have been measured by means of laser scanning. At each frequency, under the hypothesis of linear viscoelasticity, the phase velocity and attenuation of the fundamental torsional mode have been calculated as a function of the bulk shear velocity and the bulk shear attenuation of the inner core at that frequency. The resulting phase velocity and guided wave attenuation contour plots have been employed for deriving the unknown shear properties from the measured velocity and attenuation of the guided wave. The monochromaticity of the approach has not required a particular frequency dependence of the material properties to be assumed. Results for bitumen are given.     

Immunization procedures forE. coli proteins

Three immunization procedures were compared for the production of antibodies to the minor components of a complex E. coli protein (ECP) mixture: a conventional protocol and two methods that allow for the selective in vitro (cascade) or in vivo (passive) depletion of highly immunogenic proteins. An indirect ELISA showed that a maximum ELISA antibody titer was obtained with all the procedures 60 d after immunization. Analysis of these antisera by two-dimensional SDS-PAGE immunoblots, however, demonstrated that antibody reactivity to minor components in the mixture was not achieved until 112 d. This analysis also showed that a marked improvement in antibody response to minor components was obtained with the cascade immunization procedure. The mean titer and spectrum of antibody reactivity was similar for each group, and suggested that, although some individual variation was noted, the improvements observed were the result of the protocol used. Thus, for these ECPs, and multiple antigen mixtures in general, the preferred immunization protocol should employ at least three hosts and utilize the cascade immunization of Thalhamer and Freund. Characterization of the resulting antisera is best performed by use of silver stained two-dimensional SDS-PAGE and immunoblotting.     

Modified gradients for motion suppression: variable echo time and variable bandwidth

A linear algebra based deprivation is presented to demonstrate that linearly time scaling an entire gradient waveform by a factor "R" exponentially increases its sensitivity to time derivatives of position by R(i + 1), where i refers to the i-th derivative of position (e.g., i = 1 is velocity). Thus, time scaling will preserve zero valued refocussing moments associated with artifact reduction techniques designed for motion occurring between excitation and detection. Typically, gradient waveforms for artifact reduction techniques are derived for use only at specific echo times. The time scaling described here allows for simple modification of refocussing gradient waveforms for use at variable echo times. Motion sensitivity associated with non-zero moment gradient waveforms can be easily predicted and modified using this technique, with consideration for field of view, resolution, and bandwidth. A clinical example is presented showing the predicted changes in sensitivity to nonrefocussed derivatives of position as the imaging gradients are time scaled. Further, trade-offs and alternatives in sensitivity to motion, slice thickness, image bandwidth, field of view and resolution will be discussed in conjunction with time scaling. This technique will have applicability in many situations involving MRI of moving tissue and a clinical example in cardiac imaging is presented.     

Automated correction of unwanted phase jumps in reference signals which corrupt MRSI spectra after eddy current correction

A commonly applied step in the postprocessing of gradient localized proton MR spectroscopy, is correction for eddy current effects using the water signal as a reference. However, this method can degrade some of the metabolite signals, in particular if applied on proton MR spectroscopic imaging data. This artifact arises from the water reference signal in the presence of a second signal which resonates close to the main water resonance. The interference of both resonances will introduce jumps in the phase of the reference time domain signal. Using this phase for eddy current correction will result in a ringing artifact in the frequency domain of the metabolite signal over the whole frequency range. We propose a moving window correction algorithm, which screens the phase of reference signals and removes phase jumps in time domain caused by interference of signals from multiple spin systems. The phase jumps may be abrupt or gradually distributed over several time data points. Because the correction algorithm only corrects time data points which contain phase jumps, the phase is minimally disrupted. Furthermore, the algorithm is automated for large datasets, correcting only those water reference signals which are corrupted. After correction of the corrupted reference signals, normal eddy current correction may be performed. The algorithm is compared with a method which uses a low-pass filter and tested on simulated data as well as on in vivo proton spectroscopic imaging data from a healthy volunteer and from patients with a brain tumor.