Theory of spin transfer phenomena in magnetic metals and semiconductors

We propose a general theory of the spin-transfer effects that occur when current flows through inhomogeneous magnetic systems. Our theory does not rest on an appeal to conservation of total spin, can assess whether or not current-induced magnetization precession and switching in a particular geometry will occur coherently, and can estimate the efficacy of spin-transfer when spin-orbit interactions are present. We illustrate our theory by applying it to a toy-model twodimensional-electron-gas ferromagnet with Rashba spin-orbit interactions.     

Comparison of haemodynamics in cerebral aneurysms of different sizes located in the ophthalmic artery

Haemodynamics plays an important role in the progression and rupture of cerebral aneurysms. The temporal and spatial variations of the wall shear stress in the aneurysmal sac are hypothesized to be correlated with its growth and rupture. In addition, the assessment of the velocity field in the aneurysm dome and neck is important for the correct placement of endovascular coils. This work describes the flow dynamics in patient‐specific models of saccular aneurysms of different sizes located in the ophthalmic artery. The models were obtained from three‐dimensional rotational angiography image data and blood flow dynamics was studied under physiologically representative waveform of inflow. The three‐dimensional continuity and momentum equations for unsteady laminar flow were solved with commercial software using nonstructured fine grid sizes. The intra‐aneurysmal flows show complex vortex structures that change during one pulsatile cycle. A relation between the aneurysm aspect ratio and the mean wall shear stress on the aneurysmal sac is showed. Copyright © 2006 John Wiley & Sons, Ltd.     

Testing for cointegration using induced-order statistics

In this paper we explore the usefulness of induced-order statistics in the characterization of integrated series and of cointegration relationships. We propose a non-parametric test statistic for testing the null hypothesis of two independent random walks against wide cointegrating alternatives including monotonic nonlinearities and certain types of level shifts in the cointegration relationship. We call our testing device the induced-order Kolmogorov–Smirnov cointegration test (KS), since it is constructed from the induced-order statistics of the series, and we derive its limiting distribution. This non-parametric statistic endows the test with a number of desirable properties: invariance to monotonic transformations of the series, and robustness for the presence of important parameter shifts. By Monte Carlo simulations we analyze the small sample properties of this test. Our simulation results show the robustness of the induced order cointegration test against departures from linear and constant parameter models. This paper is an extension of the work of Aparicio and Granger (1995) and Aparicio and Escribano (1998).     

Synthesis of heterocyclic compounds IV1 pyrazol-1′-ylpyridines2

2-Pyrazol-1-ylpyridines were synthesized by condensation of pyridylhydrazines with 1,3-dicarbonyl compounds or by theUllmann arylation of pyrazoles with halopyridines.Taken in part from the Master's thesis ofA. A. A. Pinto, Instituto Militar de Engenharia, Rio de Janeiro, 1978.     

Efficient, accurate calculation of rotational diffusion and NMR relaxation of globular proteins from atomic-level structures and approximate hydrodynamic calculations

The calculation of the rotational diffusion tensor and NMR relaxation times of quasi-rigid macromolecular structures with atomic detail can be made by means of bead/shell models. The computing time required for calculation of these properties for a single structure using rigorous hydrodynamic methods requires a moderate computing time. In possible applications of the methodology in which such a calculation had to be repeated for many structures, a faster method would be welcome. We have studied the effect of introducing a simplifying approximation in the treatment of hydrodynamic interaction, comparing the rigorous and approximate results for a set of 30 globular proteins. When the NMR relaxation times are combined in some relative form, the rigorous and approximate results are practically coincident. For absolute quantities, such as the correlation time, we find that the bias introduced by the approximation can be closely predicted and corrected. The differences between the results of the approximate-corrected and rigorous procedures are not greater than usual experimental errors, and the typical computing time is reduced from 5 min to 1 s.     

Universal earthquake-occurrence jumps, correlations with time, and anomalous diffusion

Spatiotemporal properties of seismicity are investigated for a worldwide (WW) catalog and for southern California in the stationary case (SC), showing a nearly universal scaling behavior. Distributions of distances between consecutive earthquakes (jumps) are magnitude independent and show two power-law regimes, separated by jump values about 200 (WW) and 15 km (SC). Distributions of waiting times conditioned to the value of jumps show that both variables are correlated, in general, but turn out to be independent when only short or long jumps are considered. Finally, diffusion profiles are found to be independent on the magnitude, contrary to what the waiting-time distributions suggest.     

Synthesis of polymetallic macrocyclic terpene-derived hybrids

Terpene alkyne systems act as templates in the preparation of natural product hybrids and in macrocyclic structures having up to four terpene units and eight Co-atoms, which are built by using the Nicholas reaction.